Effects of thyrotropin-releasing hormone in vitro on thyrotropin and prolactin release from the turtle pituitary.

Effects of synthetic thyrotropin-releasing hormone (TRH) on thyrotropin (TSH) and prolactin (PRL) release by hemipituitaries of adult turtles, Chrysemys picta, were studied in an in vitro superfusion system. Significant increases in the rates of secretion of both immuno-reactive TSH and PRL occurred at doses between 0.01 and 10 ng/ml TRH.

Subcellular localization of gonadotrophic hormones LH and FSH in frog adenohypophysis using double-staining immunocytochemistry.

We applied double post-embedding immunocytochemical methods using specific antibodies against bullfrog (Rana catesbeiana) luteinizing hormone (LH) and follicle-stimulating hormone (FSH) with immunogold staining (5- and 20-nm particles) to determine the subcellular localization of both gonadotropins and to observe their immunostaining patterns in anterior pituitary of the frog Rana pipiens. Results showed that individual gonadotrophs may store either one or both gonadotropins in a given secretory granule and in large globules (lysosomes?). Most gonadotrophs (50-88%) contain both hormones; 12-50% contain only FSH, and only a few (0-7%) contain LH alone.

Specificity of amphibian and reptilian pituitaries for various forms of gonadotropin-releasing hormones in vitro.

In vitro perifusion was employed to compare the potencies of mammalian, avian, salmon, and lamprey gonadotropin-releasing hormones (GnRHs) on the release of luteinizing hormone (LH) from the pituitaries of an amphibian (Rana pipiens) and a reptile (Chrysemys picta). The chicken-I and salmon GnRH variants were equipotent with mammalian GnRH in both the frog and the turtle glands. By contrast, the lamprey GnRH was inactive (less than 1% as potent as the others).

The influence of hibernation on testis growth and spermatogenesis in the golden-mantled ground squirrel, Spermophilus lateralis.

Testis size and spermatogenesis were monitored serially in individual golden-mantled ground squirrels before, during, and after the hibernation season. During hibernation, animals spent 81% of days in torpor at body temperatures of 3-4 degrees C. Torpor bouts of 6 days duration were interspersed with brief arousals from torpor during which animals were normothermic.

The cellular basis of the calcium dependence of GnRH-stimulated gonadotropin release from frog, Rana pipiens, pituitaries.

An in vitro superfusion system was used in an attempt to identify the cellular systems involved in the Ca2+ dependence of gonadotropin-releasing hormone (GnRH) actions in the frog, Rana pipiens. Superfusion with 5 microM A23187 (a calcium ionophore) or phorbol myristate acetate (an analog of diacylglycerides) caused marked increases in luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion. Exclusion of Ca2+ from the medium prevented the stimulatory effects of PMA.

Dependence of GnRH action on Na+, K+, and Ca2+ in the frog, Rana pipiens, pituitary.

The roles of K+, Ca2+, and Na+ ions in the mechanism of gonadotropin releasing hormone (GnRH) action on frog (Rana pipiens) hemipituitaries were studied using an in vitro superfusion system. The effects of elevated K+ alone or in combination with Ca2+-depleted medium, tetrodotoxin (TTX), or with 100 ng/ml GnRH were examined. The involvement of K+ was also studied indirectly through the use of tetraethyl ammonium chloride (TEA).

Effects of temperature and mode of delivery on responses to gonadotropin-releasing hormone by superfused frog pituitaries.

An in vitro superfusion system was used to examine the effects of temperature on the responsiveness of frog, Rana pipiens, hemipituitaries to chronic superfusion with gonadotropin-releasing hormone (GnRH). The effects of pulsatile as opposed to continuous delivery of GnRH on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion were also studied at 30 degrees. Secretion of both gonadotropins (FSH and LH) increased significantly in a dose-dependent manner in response to a brief exposure to 0.

Photothermal effects on the testicular cycle in the musk turtle, Sternotherus odoratus.

A series of photothermal treatments was initiated at different times of year to examine the relative contributions of exogenous and endogenous factors affecting the timing of the testicular cycle of the kinosternid turtle, Sternotherus odoratus. Elevated temperature appeared to be the major factor stimulating testicular recrudescence (spermatocytogenesis, spermiogenesis, and, to some extent, androgen secretion). However, depending on the time of year, short or long daylengths, in conjunction with elevated temperatures, enhanced testicular responses (recrudescence or regression).

Seasonal cycles in gonadal activity and plasma gonadotropin in the musk turtle, Sternotherus odoratus.

Plasma gonadotropin cycles were examined in relation to the seasonal gonadal cycle in freshly captured musk turtles, Sternotherus odoratus, from South Carolina. Acute and chronic stress effects of captivity on testicular growth and circulating plasma testosterone (T) and follicle-stimulating hormone (FSH) also were examined. Monthly mean FSH levels in freshly captured males were correlated significantly with plasma T.

In vitro ovarian responses to pulsatile and continuous gonadotrophin administration on steroid secretion and oocyte maturation in the frogs, Rana pipiens and Rana catesbeiana.

An in vitro superfusion system was used to study the relative effects of pulsatile and continuous gonadotrophin administration on steroid secretion and oocyte maturation in Rana pipiens ovaries. Pulsatile (10 min pulse/hr) delivery of pituitary extract (PE) resulted in a slightly (insignificantly) lower level of testosterone (T) secretion over a 12-hr period. Administration of a fivefold lower, subliminal amount of PE instead of hormone-free media between pulses did not change the pattern of T secretion.

Suitability of the mammalian model in comparative reproductive endocrinology.

Perhaps one should be impressed by the basic generality of many of the features of the mammalian HHG system. The applicability of this model to other groups argues for the generally conservative nature of the basic organization of the reproductive endocrine system. Even in cases where exceptions are apparent, we must be cognizant of the relatively narrow base of mammalian species on which the classical mammalian model is built.

Effects of cycloheximide on in vitro testosterone secretion from RANA catesbeiana ovaries.

A 1 hr exposure to 20 micrograms/ml of the protein synthesis inhibitor, cycloheximide (CHX), essentially abolished secretion of testosterone (T) by bullfrog ovarian fragments during simultaneous administration of homologous pituitary extract and CHX. Removal of CHX from the medium after 4 hr of treatment reversed the inhibition of T secretion, allowing it to attain control levels. Pre-exposure of ovarian fragments to CHX was not required to obtain an inhibition of T secretion.

Effects of gonadectomy and steroid treatment on plasma gonadotropins and the response of superfused pituitaries to gonadotropin-releasing hormone in the turtle Sternotherus odoratus.

Gonadectomized (gonadex) turtles, Sternotherus odoratus, had significantly elevated plasma FSH, but LH was less consistently affected. Estradiol (E2)-implants suppressed plasma FSH in gonadex females but not in males: testosterone (T) partially suppressed FSH in males. In contrast, E2-treatment markedly suppressed pituitary LH content and in vitro LH secretion in gonadex and intact turtles (inhibitory effects of E2 were less in intact than ovariectomized females).

In vitro study of the direct ovarian effects of gonadotropin-releasing hormone (GnRH) in the frogs, Rana pipiens and Rana catesbeiana.

Ovaries from the leopard frog, Rana pipiens, and bullfrog, R. catesbeiana, were used to study potential direct extrapituitary effects of gonadotropin-releasing hormone (GnRH). GnRH alone did not alter steroid secretion from ovaries in either species.

In vivo and in vitro responses to gonadotropin releasing hormone in the turtle, Chrysemys picta, in relation to sex and reproductive stage.

In vivo and in vitro responsiveness to gonadotropin releasing hormone (GnRH) was studied in the turtle, Chrysemys picta, after manipulation of reproductive condition by temperature: Warm temperatures (28 degrees) induced testicular growth and ovarian regression compared to cold (17 degrees) treatment. Only males (and primarily from cold treatment) responded to GnRH injection (40 micrograms/100 g body wt intracardiac); correlated increases occurred in plasma LH and testosterone. Effects of GnRH (10 and 100 ng/ml) on LH and FSH secretion by hemipituitaries were studied in a superfusion system; tissues responded to between 0.

LH secretion in response to gonadotropin releasing hormone (GnRH) by superfused pituitaries from two species of turtles.

A superfusion system was employed to study the dynamics of the responses of LH secretion to gonadotropin releasing hormone (GnRH) by anterior pituitary glands (quartered) from adult turtles, Pseudemys scripta and Chrysemys picta. Responsiveness was highly variable in both species, but in many cases, the tissues showed marked responses to relatively low doses (2-20 ng/ml) of GnRH. GnRH had no effect on LH secretion in five female P.

Pituitary responsiveness to superfused GnRH in two species of ranid frogs.

Dynamics of pituitary responsiveness to gonadotropin-releasing hormone (GnRH) as measured by LH and FSH secretion rates were examined for two species of ranid frogs in an in vitro superfusion system. The influence of sex was studied with juvenile bullfrogs, Rana catesbeiana, and responsiveness to long-term continuous superfusion with GnRH was examined in R. catesbeiana and R.

Seasonal cycles in testicular activity, gonadotropin, and thyroxine in the painted turtle, Chrysemys picta, under natural conditions.

Plasma levels of testosterone (T), thyroxine (T4) and follicle-stimulating hormone (FSH) were measured in a field population of the painted turtle, Chrysemys picta, in Michigan. All three hormones showed pronounced seasonality; plasma luteinizing hormone (LH) remained nondetectable. Plasma T and FSH concentrations were highly correlated and exhibited biphasic cycles with peaks in spring and fall, whereas T4 showed a single peak in summer, coincident with the nadir in T.

Reevaluation of the relative activities of the pituitary glycoprotein hormones (follicle-stimulating hormone, luteinizing hormone, and thyrotrophin) from the green sea turtle, Chelonia mydas.

The discovery that the follicle-stimulating hormone (FSH) previously prepared from the green sea turtle, Chelonia mydas, contained a major neurohypophysial contaminant prompted a repurification and characterization of the glycoprotein hormones in this turtle. Results reaffirmed the physicochemical distinctiveness of the three hormones. Minimal cross-contamination between hormones (less than 2%) was achieved by ion-exchange chromatography, subunit dissociation (of contaminating luteinizing hormone (LH], gel filtration, and immuno-affinity chromatography.

Changes in hormone levels in relation to breeding behavior in male bullfrogs (Rana catesbeiana) at the individual and population levels.

Fluctuations in plasma androgen (testosterone and 5 alpha-dihydrotestosterone), corticosterone (B), and luteinizing hormone (LH) of male bullfrogs in central California were measured during the spring mating season. Androgen and LH levels generally increased in the population prior to the initiation of chorusing and establishment of territories, whereas plasma B peaked in a 2-week period at the start of heavy chorusing; this coincided with a transitory, 1 week decline in androgen. Individual males showed fluctuations in plasma androgen and LH levels throughout the breeding season, often within 1 day, but there was no clear correlation between changes in the two hormones.

Annual and diurnal cycles in plasma testosterone and thyroxine in the male green sea turtle Chelonia mydas.

Male plasma testosterone (T) and thyroxine (T4) were monitored over several annual cycles in a captive breeding colony of green sea turtles, Chelonia mydas. Daily and annual water temperatures varied by only approximately 1 and 3 degrees, respectively. A pronounced season cycle in plasma T was evident in the population as a whole and in individual animals: plasma T was at a nadir (approximately 3 ng/ml) in September-November and then increased progressively to a peak (27-39 ng/ml) in April; levels began declining immediately thereafter, coincident with the onset of copulatory behavior.

Steroid biosynthesis in turtle testes.

Testicular metabolism of radiolabelled substrates (pregnenolone, progesterone and androstenedione) was examined in two species of turtles, Pseudemys scripta and Sternotherus odoratus. Chemical methods (chromatography, derivative formation and crystallization) identified testosterone (in both species) and 5 alpha-androstane-3 beta,17 beta-diol (in S. odoratus) as products.

Studies on the specificity of thyroid response to pituitary glycoprotein hormones.

Thyrotropins (TSH) and gonadotropins (luteinizing hormone, LH, and follicle-stimulating hormone, FSH) purified from ovine, bovine, ostrich, sea turtle, and bullfrog pituitary glands were tested for their ability to simulate the thyroid glands of four species of amphibians (three anurans and a urodele), a reptile (the slider turtle), and a bird (the cockerel). All animals tested responded specifically to mammalian, sea turtle, and ostrich thyrotropins; any thyroid-stimulating activity of the gonadotropins from these species could be accounted for by their contamination with thyrotropin. In addition, the three anuran species showed a high degree of specificity for bullfrog TSH; bullfrog LH exhibited low thyrotropic activity in amphibians.

Presence of a neurophysin-like precursor in the green turtle (Chelonia mydas).

A glycoprotein of neurohypophysial origin was found to have cofractionated with FSH prepared from pituitary glands of the green turtle, Chelonia mydas. Antiserum raised against this preparation contained high antibody titres and affinity for the neurohypophysial component and allowed development of a specific radioimmunoassay to monitor its purification and distribution in the brain. Immunocytochemistry revealed that the glycoprotein was concentrated in the pars nervosa and associated nerve tracts passing through the median eminence to the supraoptic and paraventricular nuclei; similar distributions were observed in turtles and rats.

The role of androgen in the development of sexual differences in pituitary responsiveness to gonadotropin releasing hormone (GnRH) agonist in the bullfrog, Rana catesbeiana.

Sexual differences in pituitary responsiveness to acute injection of gonadotropin-releasing hormone (GnRH) agonist, as measured by increments in plasma FSH and LH, were examined throughout development in the bullfrog, Rana catesbeiana. Untreated tadpoles, in various stages of metamorphosis, were unresponsive to GnRH agonist. Postmetamorphic males showed a progressive increase in the magnitude of pituitary response with age, whereas females remained relatively insensitive until after sexual maturation; males were always more responsive than females.