Elevation of serum testosterone during chronic LHRH agonist treatment in the bull.

The objective of this study was to try to depress serum testosterone (T) in bulls by prolonged treatment with a potent luteinizing hormone-releasing hormone (LHRH) agonist. Eight sexually mature bulls (325 to 475 kg) were assigned to treatment or control groups. Treatment consisted of 150 micrograms nafarelin acetate 6-D-2-naphthyl-alanine-LHRH (LHRH-A) injected im every 6 h for 15 d.

Nursing enhances the negative effect of estrogen on LH release in the cow.

Twenty-three crossbred beef cows between 4 and 5 yr of age were assigned at random to one of six treatments: (1) ovariectomized 4 d postpartum (OVX) with early weaning of calves 21 d postpartum (OVX-EW; n = 4), (2) OVX-EW and 17 beta-estradiol implants (OVX-E2-EW; n = 4), (3) OVX and normal nursing by calves throughout the experiment (OVX-NN; n = 3), (4) OVX-NN and 17 beta-estradiol implants (OVX-E2-NN; n = 4), (5) intact cows and early weaning of calves 21 d postpartum (EW), (6) intact cows and normal nursed (NN). Blood was collected at 15-min intervals over a 4-h period once weekly during the 12-wk postpartum period in the OVX cows. Early weaned intact cows exhibited estrus 23 d sooner (P less than .

Effects of photoperiod and estradiol on tonic gonadotropins in ovariectomized ewes.

Estradiol-17 beta (estradiol) inhibition of tonic (basal, as opposed to cyclic or preovulatory) serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) was evaluated in ewes subjected to long or short photoperiods. Nine mature Colombia ewes were ovariectomized early in the breeding season and implanted with either Silastic capsules containing approximately .12 g of estradiol (n = 4) or with empty capsules (n = 5).

Pituitary and ovarian luteinizing hormone releasing hormone receptors during the estrous cycle, pregnancy and lactation in the rat.

Female Sprague-Dawley rats were decapitated at various stages of the estrous cycle, pregnancy, lactation and following ovariectomy. Anterior pituitary and ovarian tissues were collected and assayed to quantify luteinizing hormone releasing hormone (LHRH) receptors. No changes were noted in receptor affinity either between tissues or physiological stages studied.

Evaluation of pituitary responsiveness to LHRH as a pregnancy test in ewes.

Pregnant and nonpregnant ewes were injected with luteinizing hormone-releasing hormone (LHRH). Pituitary responsiveness, based on serum luteinizing hormone (LH), and follicle stimulating hormone (FSH) concentration, 2 hr after injection was then determined for each ewe, by radioimmunoassay (RIA) and correlated with the physiological reproductive state of each ewe. The serum LH release in pregnant ewes was significantly lower than that in nonpregnant ewes.