Preliminary evidence of a synergistic alpha 1- and beta 1-adrenoceptor regulation of rat pineal hydroxyindole-O-methyltransferase.

The activity of serotonin N-acetyltransferase in the rat pineal is regulated through a synergistic action of norepinephrine on alpha 1- and beta 1-adrenoceptors. Rat pineal hydroxyindole-O-methyltransferase (HIOMT) activity is also responsive to the beta 1-adrenoceptor, while melatonin synthesis and indoleamine release in certain species is apparently under alpha 1-adrenoceptor control. The present study reports that the simultaneous administration of doxazosin (a selective alpha 1-adrenergic antagonist) and metoprolol (a selective beta 1-adrenergic antagonist) reduces peak HIOMT activity significantly more than either agent alone, indicating that rat pineal HIOMT is also subject to synergistic alpha 1- and beta 1-adrenergic regulation.

The effect of neonatal pinealectomy on the inhibitory actions of food restriction on vaginal opening and collagen aging in the rat.

Long-term food restriction is known to inhibit development and aging in the rat. These actions may be mediated by the pineal hormone, melatonin, whose secretion is increased by food restriction. This mechanism was investigated by studying the effects of pinealectomy in ad libitum fed and food restricted rats of both sexes living under normal conditions of temperature (23 degrees C) and lighting 12 h light:12 h dark cycle) over a period of 400 days.

A distinct diurnal rhythm in hydroxyindole-O-methyltransferase (HIOMT) activity in the male albino rat.

Pineal hydroxyindole-O-methyltransferase (HIOMT) has been reported to show a diurnal rhythm activity in the rat, although this is not fully confirmed. The present study reexamines this issue and reports a distinct diurnal rhythm in rat pineal HIOMT. Peak enzyme activity occurs 5 hr after the onset of darkness, followed by two lesser bursts of activity preceding each change in the photoperiod.

The use of hypothermia in surgical pinealectomy of the neonate rat.

A technique is described in which rat pups (5-7 days old) are induced into a state of suspended animation by placing them in the freezing compartment of a refrigerator at -20 degrees C for 8-10 minutes. This induces cessation of respiration and heart beat for 12-15 minutes. Surgical pinealectomy is undertaken during this period.

Investigation of circadian rhythms for pineal 5-hydroxytryptophol and other indoles in the rat.

5-hydroxytryptophol (5HTL) occurs in the pineal gland of the rat at levels comparable to those of melatonin, yet few studies have been conducted to investigate 5HTL as a potential alternative pineal hormone. In this study the pineals of 90-day-old male Sprague Dawley rats have been assayed by high performance liquid chromatography coupled with electrochemical detection. Significant (P less than .

Maternal and larval effects of photoperiod on the induction of larval diapause in two species of fly, Calliphora vicina and Lucilia sericata.

The induction of larval diapause in the blowflies Calliphora vicina and Lucilia sericata was studied in relation to maternal and/or larval exposure to photoperiod. In C. vicina, maternal experience of short daylength was shown to be more important than larval exposure, although diapause was only observed when the larval rearing temperature was below 15 degrees C.

Pineal indoles: significance and measurement.

Despite intensive investigation, particularly over the past fifteen years, many aspects of pineal function with respect to mammalian physiology remain obscure. Much of this work is reviewed and particular attention focussed on indole metabolism within the pineal gland. Emphasis is placed on the development of new analytical techniques with special reference to high performance liquid chromatography coupled with electrochemical detection.

Plasma thyroid hormone and glucocorticosteroid concentrations in the male rat following prolonged exposure to stress.

Exposure of male CSF rats to a signalled unpredictable 60-day stress regimen induced a significant elevation in circulating triiodothyronine (T3) concentration above the control for the first 20 days of stress before the rate of secretion returned to normal. On the other hand, circulating thyroxine (T4) concentration fell significantly below the control value for the first 5 days of stress before the normal rate of secretion was reached in 10 days. A histological study of the thyroid gland revealed no change in activity among any of the control and stressed groups.

The effect of sulfinpyrazone on morphological changes in the coronary vasculature induced by prolonged unpredictable stress in the rat.

It was confirmed that prolonged unpredictable stress in the rat induces morphological change in the coronary microcirculation. These changes include dilation in venules, deposits staining positive with PAS in the venules due to platelet aggregation and a breakdown of the endothelial lining in arterioles. Sulfinpyrazone is reported to prevent platelet agglutination, and shows effectiveness in the clinic in preventing re-infarction following infarction.

The action of nicotine on the pituitary-adrenal cortical axis.

Nicotine was found to raise dramatically plasma corticosterone levels in a dose-dependent manner. Plasma corticosterone time course for the 100 microgram/kg dose of nicotine produced an initial increase in corticosterone elevation which did not return towards control levels until after 30 min. The 200 and 500 microgram/kg doses, however, indicated a biphasic response for nicotine-induced steroid secretion.

Ultrastructural changes in the adenohypophysis, adrenal gland activity, and desynchronization of the oestrous cycle following unpredictable stress in the rat.

An ultrastructural study of the adenohypophysis, after exposure of female Wistar rats to a signalled unpredictable 5- and 15-day stress regimen, is described. Cellular activity of the adenohypophysis correlated well with the circulating levels of corticosterone. Intense secretory activity was observed in all tropic cell types at 5 and 15 days although the observed differences generally were greater in the 5-day stressed group.

Changes in the coronary vascular system following prolonged exposure to stress.

Hearts of stressed rats showed marked changes in the coronary vasculature. It was suggested that such morphological changes could be explained on the basis of an increased coronary vascular permeability. Endogenous inflammatory substances could induce swelling of the endothelial cells and cause separation of the neighbouring cells from one another, thus allowing the passage of lipid molecules through the endothelial lining.

Effect of stress on the uptake of 3H-norepinephrine into rat myocardium.

Spontaneously beating atria from rats previously exposed to irregular, signalled footshock were incubated with 3H-norepinephrine. A significant reduction in the uptake and retention of radioactivity was found in the atria from stressed animals compared with unstressed controls. A kinetic study of the uptake process in both the stressed and control groups showed a similar Km value but a significantly different Vmax.

Endogenous levels of catecholamines in the rat myocardium following exposure to stress.

Following exposure of male rats to irregular signalled footshock from which they could escape, the endogenous level of norepinephrine in the myocardium was significantly reduced. In atria the depletion of endogenous norepinephrine was significant following 1 day of stress. This significant depletion was maintained following 4 days of stress but began to return towards control levels by Day 10.

Myocardial sensitivity to catecholamines following exposure of rats to irregular, signalled footshock.

Emotional stress is associated with an increased activity of both the pituitary-adrenal cortical system and the sympathetic-adrenal medullary systems resulting in raised plasma levels of glucocorticoids and catecholamines. There is evidence to suggest that prolonged stress induced adrenergic hyperactivity initiated myocardial pathogenesis and that this may relate to a corticosteroid catecholamine interaction. In the present study driven atrial strips removed from stressed male CSF rats were found to exhibit an enhanced sensitivity to both norepinephrine and epinephrine.