Effect of neonatal castration on the content of hypothalamic LHRH, pituitary LH and plasma LH in developing male rats.

The content of hypothalamic LHRH and concentration of LH in pituitary and plasma were measured on day 5, 7, 10, 14, 17, 22, 25, 30, 45, 52 and 60 in male rats which were bilaterally castrated on day 2. The levels of plasma LH were significantly higher in all the groups of castrated rats than in normal male rats of corresponding ages. The concentration of plasma LH did not rise progressively but showed day to day fluctuation apparently due to alteration of sexual differentiation of the hypothalamus. The concentration of pituitary LH was significantly lower in neonatally castrated rats compared to normal male rats except on days 17, 25 and 30. The content of hypothalamic LHRH declined initially following castration, but from day 17 onwards significantly higher levels of hypothalamic LHRH were maintained in neonatally castrated rats than in intact control. Initial decline in the content of hypothalamic LHRH may be because of stimulation of release of LHRH which exceeds maximal rate of synthesis and subsequent increase in the content of hypothalamic LHRH may be due to enhanced LHRH synthesis as a result of castration.     

Changes in pituitary and ovarian LHRH receptors after active immunization of female rats against LH or LHRH

The hypothalamic-pituitary-ovarian axis of female rats was disrupted at the site of LHRH stimulation by active immunization against LHRH or at the site of LH action by active immunization against LH. Active immunization against LH was associated with an increase in pituitary LHRH receptors to levels comparable to control values at pro-oestrus whereas immunization against LHRH led to a marked reduction in receptor numbers. Ovarian LHRH receptor concentrations were increased by both treatments. It is concluded, therefore, that (1) LHRH receptors in the pituitary and ovary are not concomitantly controlled, and (2) pituitary receptor numbers are primarily under positive autoregulatory control by LHRH and that ovarian LHRH receptor concentrations may be under long-term influence of LH.     

Pituitary LH response to LHRH in male rats following pentobarbital anesthesia

Plasma LH concentrations were determined in unanesthetized or pentobarbital (PB) anesthetized male rats following several doses of LHRH administered into the lateral ventricle of jugular vein. Regardless of the route of injection of LHRH, plasma LH concentrations were similar whether animals received PB anesthesia or not. No evidence was found that PB enhanced or diminished the response of the pituitary to LHRH in male rats.     

Effects of microinjection of various prostaglandins into the 3rd ventricle, median eminence and pituitary on plasma LH in rats.

The effects of microinjection of PG'S (PGE1, E2, F2a) into the 3rd ventricle, median eminence (ME) and anterior pituitary on plasma LH in rats were investigated. Blood samples were obtained by jugular puncture before, and 10 and 45 min after the injection of PGS (50 or 100 mug), plasma LH was measured by radioimmunoassay. In the 3rd ventricle microinjection, PGE2 prodiced a significant rise in plasma LH. PGE1 and F2a did not significantly after plasma LH levels. In the median eminence, PGE2 and E1 produced a significant rise in plasma LH. PGF2a did not alter plasma LH levels. In the pituitary, PGE2 and E1 produced a significant rise in plasma LH. PGF2a did not alter plasma LH levels. These observations indicate that PGs act directly on the hypothalamic-pituitary axis, and that particular PG may be involved in the release of particular horomones from the hypothalamus and pituitary.     

Modulation of pituitary responsiveness to LHRH by androgens in ovariectomized female rats.

The effect of androgens on pituitary response to luteinizing-hormore-releasing hormone (LHRH) and their ability to modify effects of 17beta-estradiol (E2) on pituitary responsiveness to LHRH were tested in ovariectomized rats maintained on a daily dose of 0.25 microgram estradiol benzoate per rat for 6 d before androgen administration. Testosterone propionate (TP) (4, 40, 400, or 4000 microgram per rat), administered 24 h before LHRH (500 ng per rat), had no significant effect on luteinizing hormone (LH) or follicle-stimulating hormone (FSH) response. Similar doses of dihydrotestosterone (DHT) did not significantly alter the LH response but significantly suppressed the FSH response. Even the lowest dose completely blocked the FSH response to LHRH. TP in combination with 4 or 400 microgram of E2 suppressed the stimulatory effect of E2 on both LH and FSH response to LHRH in a dose-related manner. DHT and E2 in combination affected LH response inconsistently, whereas their ratio determined FSH response; there was pronounced inhibition of FSH response in rats given high doses of DHT combined with low doses of E2; DHT inhibition of FSH response in animals receiving 4 microgram of DHT with 400 microgram E2 was partially overcome by the stimulatory effect of E2. Our results indicate that TP and DHT affect LH and FSH response to LHRH differently. The ratio of androgen to estrogen is important in determining the response to LHRH.     

Comparative ability of chicken and mammalian LHRH to release LH from rooster pituitary cells in vitro

Biological properties of homogeneous solutions of chicken (c) and mammalian (m) LHRH were compared by their ability to release LH, in vitro, from a rooster pituitary cell incubation system. Homogeneity of the two LHRH species was confirmed by High Performance Liquid Chromatography (HPLC) using linear gradients of acetonitrile and phosphate buffer. A clear HPLC separation of [Gln8]-LHRH ( cLHRH ) and [Arg8]-LHRH ( mLHRH ) was obtained, with the former having a consistently longer retention time than the latter. cLHRH cause a greater (p less than .025) in vitro release of LH at low doses (less than 1 ng/2 X 10(5) live pituitary cells), but not at high doses (greater than 10 ng/2 X 10(5) live pituitary cells), than that caused by mLHRH . Our results indicate that rooster pituitary cells are significantly more sensitive to low doses of cLHRH than to similar doses of mLHRH , when assessed by their ability to release LH in vitro.     

Effects of an LHRH agonist on endocrine function, LHRH receptor and LH/hCG receptor in the pituitary-gonadal axis of male rats

The effects of an LHRH agonist (LHRHa), [D-Ser (tBu)]6 des-Gly-NH210) ethylamide, on endocrine function and the LHRH and LH/hCG receptors in the pituitary-gonadal axis were examined. The LHRHa was injected at 100 ng/100 g body weight into male rats once a day for 4 weeks and its effects were observed until 2 weeks after the end of treatment. Due to LHRHa treatment, the plasma LH concentration began to increase on day 3, reached a peak on day 7, and then decreased, although it remained above the control level during the treatment. The pituitary LH content decreased on day 1, reached a minimum (about 40% of the control) between days 3 and 7, and then was maintained at 60% of the control level until week 4. In contrast, the pituitary LHRH receptor concentration increased only on day 3, and the association constant (Ka) remained unchanged during the observation period. The testis weight and plasma testosterone concentration began to decrease on day 3, reached the minimum on day 7 and remained at this level until week 4, and their levels were not completely restored to normal 2 weeks after cessation of treatment. The testicular LH/hCG receptor concentration was decreased on day 1, and markedly decreased to 10-15% of the control value between day 7 and week 4, but the Ka value was slightly increased during the treatment. However, these values had completely recovered 2 weeks after the cessation of treatment. The testicular LHRH receptor concentration increased between days 1 and 7, returned to the control level in weeks 2 and 4, and then decreased 2 weeks after cessation of treatment. Its Ka value was reduced in weeks 2 and 4. These data suggest that the inhibitory effect of LHRHa on the gonad in male rats is not due to reduced pituitary LH release, but to changes in the number and Ka values of gonadal receptors for LH/hCG and LHRH.     

Effect of LH, FSH, LH + FSH and homoplastic pituitary extract on developing testis and epididymis of pigeon Columba livia

Ovine LH is needed for differentiation of juvenile Leydig cells and for their maintenance and steroidogenic potential, while FSH is necessary for Sertoli cell activity and spermatogonial multiplication suggesting that LH is steroidogenic hormone and FSH is gametogenic in the developing pigeon, C. livia. Homoplastic pituitary extract is more potent than ovine LH + FSH in stimulating gametogenic and endocrine components of the developing testis.     

Effect of LHRH on plasma 7B2 in patients with gonadotropin-producing pituitary adenomas.

Plasma immunoreactive (IR)-7B2 was measured in four patients with gonadotropin-producing pituitary adenomas. The basal level of plasma IR-7B2 was elevated in one of the four patients. Hyperresponse of plasma IR-7B2 to LHRH or LHRH/TRH was noted in two patients tested. 7B2 was positively stained in a paraffin-embedded section of gonadotropin-producing pituitary adenoma obtained at surgery. These findings suggest that 7B2 is produced in gonadotropin-producing pituitary adenomas and secreted into the blood stream under certain conditions. 7B2 may be a useful marker for gonadotropin-producing pituitary adenomas.     

Correlation between LH and estrogen receptor turnover in pituitary and hypothalamus of castrate rats following estrogen agonists and antagonists

A series of studies was undertaken to correlate the short-term dynamics of LH secretion and depletion-replenishment patterns of estrogen receptors (ER) in hypothalamic and pituitary cytosols of ovariectomized rats. Animals castrated for 2 weeks were administered various test compounds and analyzed at 1, 3, 5, 10 and 15 h post-treatment. A single injection of 10 micrograms 17 beta-estradiol (E2) to ovariectomized rats elicited a rapid depletion of ER in both pituitary and hypothalamus and a dramatic, though delayed, fall in serum LH. ER replenishment occurred in both tissues through 15 h and LH recovered in a similar manner. When cycloheximide was administered along with E2, ER replenishment was completely inhibited in both tissues; serum LH fell and failed to recover. Actinomycin D injected with E2 blocked replenishment in pituitary but not hypothalamus; serum LH recovered in parallel with the hypothalamic ER pattern. 17 alpha-E2 elicited only slight changes in ER and LH was suppressed 10-20% through 15 h. CI-628 caused a near total depletion of pituitary ER with no subsequent replenishment, whereas hypothalamic ER content was virtually unaltered; serum LH was suppressed and later recovered. Orchidectomized rats given 5 micrograms E2 demonstrated a less complete ER depletion in hypothalamus, and an earlier replenishment than that seen in pituitary or hypothalamus of similarly treated ovariectomized females. Serum LH rebounded to 157% of control levels at 15 h. The results indicate that the acute feedback suppression of LH by exposure to estrogens correlates with binding to ER and nuclear translocation. Replenishment and/or retention of cytoplasmic ER in hypothalamus appears to be required for full resumption of LH secretion, following acute suppression.     

Hypothalamic luteinizing hormone-releasing hormone (LHRH) and LH secretion in aging female rats

Age-related changes in hypothalamic luteinizing hormone-releasing hormone (LHRH) and luteinizing hormone (LH) secretion were studied in young (6 months), middle-aged (12 months) and old (18 months) female rats. The LHRH levels in the mid-hypothalamic area were higher in intact middle-aged and old females than in young ones. Additionally, there was no age difference in the hypothalamic LHRH levels in male rats. In order to clarify the significance of this age-related increase in female rats, we examined the effects of progesterone treatment in estrogen-primed ovariectomized young and old rats on the LHRH levels in the median eminence (ME) and on plasma LH levels. We found phasic changes in ME-LHRH and plasma LH levels in estrogen-primed rats following progesterone treatment in rats of both ages, but the progesterone-induced change in ME-LHRH levels tended to be delayed in old rats compared with young females. This delay may correspond to the delayed onset, slow and low magnitude of plasma LH increase in old females. The ME-LHRH levels were generally higher in old rats than in young rats. Nevertheless, we found that the increase in plasma LH in response to progesterone treatment in estrogen-primed ovariectomized females was smaller in old rats than young rats. These results suggest that the LHRH secretory mechanism changes with age in female rats. Such alterations may result in the accumulation of LHRH in the mid-hypothalamic area and an increase in ME-LHRH.