Delayed Effects of in Vivo LHRH Immunoneutralization on Gonadotropins and Prolactin Secretion in the Female Rat

Abstract

A single ip injection (0.2 ml) of a rabbit antiserum to LHRH was given at noon on proestrus (day 0) to 4-day cycling rats. A blockade of the preovulatory surge of LH and FSH was observed, as well as inhibition of ovulation; the prolactin (PRL) surge was unaffected. Four days later, palsma LH and FSH were still low and hypoprolactinemia appeared, while the estrous cycle was unaffected. Then, after a transient diestrous period, vaginal smears indicated a pattern of persistent estrus for at least 240 days starting from day 8 after treatment. Hypothalamic LHRH remained low throughout this period, with the exception of a transient rise around day 36; hypothalamic serotonin and dopamine were unchanged. A peak of FSH in serum appeared on day 28 and an elevation of serum LH on day 36; this latter rise was concomitant with the increase of hypothalmic LHRH and with ovarian luteinization. Except for this short period, the ovaries showed a picture of persistent estrus, with large, cystic follicles. During the whole experimental period, basal serum FSH levels were higher than those of LH. Pituitary FSH and LH contents remained in the range usually found during the normal estrous cycle. Starting from the 8th day after treatment, a marked hyperprolactinemia appeared. Serum estradiol and progesterone were assayed on days 10 and 40 after injection; no significant increase in either steroid was observed on day 10, but on day 40 the levels of estradiol increased to values similar to those of progestrus, while progesterone showed only a small, but significant, increase. Thus, a single injection of LHRH antiserum (AS) in a normal cycling rat provoked a long-term alteration in hypothalamic function. The results so far obtained suggest that the long-lasting hyperprolactinemia induced by this treatment, might be due to an abnormal ovarian secretion.

Circadian and Cyclic LHRH Variations in the Organum vasculosum of the Lamina Terminalis of Female and Male Rats

“…The pattern of daily fluctuations of MBH LHRH, found by the above-mentioned authors, is similar to that we found in the OVLT, i.e., there are two daily peaks in the MBH as well as in the OVLT on the day of P, one in the morning between 11.00 and 12.00 h and one in the late after noon. The preovulatory peak of LHRH on the day of P cor relates well with the observations on the pituitary LH and FSH levels, where the peak is 1 h later than the hypothalam ic LHRH peak [19], Present findings (both immunohistochemical and RIA observations) also indicate that the OVLT exhibits changes during the sexual cycle. Cyclic changes were also found in the histograms of vesicle diameters and in the number of vesicles in the nerve terminals of the OVLT.…”

Variations in Plasma Levels of Substance P and Effects of a Specific Substance P Antagonist of the NK₁ Receptor on Preovulatory LH and FSH Surges and Progesterone Secretion in the Cycling Cynomolgus Monkey

“…In contrast, no significant effects on the FSH surge were observed. A dissociation in the reduction of preovulatory LH and FSH release has been previously observed in other experimental situations such as the immunoneutralization of circulating levels of GnRH [46]during the morning of proestrus in the cycling female rat. The present study demonstrates for the first time a potentiating role of SP-ergic transmission on the preovulatory LH surge in the cynomolgus monkey by a specific action through NK 1 receptors.…”

Differential effects of LH-RH immunoneutralization on LH and FSH secretion in the ewe

“…Passive immunoneutralization of luteinizing hormone-releasing hormone (LH-RH) prevents the preovulatory surge of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the rat (Koch, Chobsieng, Zor, Fridkin & Lindner, 1973;Arimura, Debeljuk & Schally, 1974;Kerdelhue, Catin, Kordon & Jutisz, 1976; Kawakami & Higuchi, 1979), hamster (de la Cruz, Arimura, de la Cruz & Schally, 1976) and ewe (Narayana & Dobson, 1979;Fraser & McNeilly, 1982). However, little is known about the changes associated with neutralization of LH-RH on tonic gonadotrophin secretion in the intact female.…”