William E. Bridson

Effects of Discrete Lesions of Preoptic and Suprachiasmatic Structures in the Female Rat

The purpose of this study was to determine which specific structures within the medial preoptic-anterior hypothalamic area are necessary to maintain cyclic ovulation in the rat, and to define the deifcit(s) in the feedback regulation of gonadotropin secretion associated with lesions that result in anovulation. Large (approximately 1.1 mm dia.) or small (approximately 0.7 mm dia.) electrolytic lesions were placed in several loci within preoptic, anterior hyopthalamic and suprachiasmatic areas in regularly cycling adult female rats. Large lesions which included the suprachiasmatic nuclei (SCN) induced an anovulatory condition characterized by persistent vaginal cornification and polyfollicular ovaries (persistent estrus). Large or small lesions which included the medial preoptic nucleus (MPN), a small periventricular column of cells located immediately caudal to the organum vasculosum of the lamina terminalis (OVLT), also induced persistent estrus. Lesions placed elsewhere within the medial preoptic-anterior hypothalamic area never induced persistent estrus but were frequently associated with repeated periods of prolonged diestrus separated by brief periods of vaginal cornification. These prolonged diestrous intervals appeared to be related to spontaneous luteal activation following ovulation rather than impaired folliculogenesis. LH and FSH surges induced by sequential administration of estradiol benzoate and progesterone (P) were completely abolished only by lesions which included the MPN. Small lesions involving only the MPN and OVLT or the MPN and caudally adjacent loci in the suprachiasmatic region were as effective in this respect as larger lesions encompassing most of the preoptic-suprachiasmatic region from the diagonal band of Broca to the rostral pole of the SCN. On the other hand, P-induced gonadotropin surges were never completely blocked by SCN lesions, although the magnitude of the surge was highly variable and frequently attenuated compared to controls. It is concluded that both the MPN and SCN are required for the long-term maintenance of spontaneous cyclic ovulation in the rat. However, the characteristically dissimilar deficits in P-induced gonadotropin release associated with lesions of one or the other of these structures indicate that these nuclei may play different roles in the regulation of gonadotropin surges. It is suggested that neural elements indispensable for phasic gonadotropin release are located within and/or immediately adjacent to the MPN. The SCN may influence phasic gonadotropin release indirectly, by regulating circadian rhythms which govern the responsiveness of other neural elements to hormonal stimuli.

Role of Brain Monoamines in Release of Gonadotropin before Proestrus in the Cyclic Rat

To determine whether brain monoaminergic neurons are involved in the release of gonadotropins responsible for estrogen increases before proestrus, various inhibitors and precursors of monoamine biosynthesis were administered subcutaneously or intracranially to the 3rd ventricle at 10.00 or 20.00 on the day before proestrus, the 2nd day of diestrus (DII) in 4-day cycling rats. The inhibitors used were alpha-methyl-p-tyrosine (alpha-MPT) and bis-(4-methyl-1-homopiperazinyl-thiocarbonyl)-disulfide (FLA-63). The effects of these drugs on changes in vaginal cytology, ovulation, uterine weight of uterine intraluminal fluid, and on serum concentrations of LH and FSH were evaluated in selected experiments. (1) Administration of alpha-MPT (150 mg/kg s.c.), an inhibitor of tyrosine hydroxylase, at 10.00 on DII reduced weights of uterus and intraluminal fluid on the day of expected proestrus (P), prevented vaginal cornification on estrus (E), blocked ovulation in all 10 rats, and induced prolonged diestrus. (2) Administration of FLA-63 (10 mg/kg s.c.), an inhibitor of dopamine-beta-hydroxylase, at 10.00 on DII reduced weights of uterus and intraluminal fluid on P, blocked ovulation for a few days but did not prevent vaginal cornification at the expected time of E. (3) Administration of alpha-MPT (200 mg/kg) or FLA-63 (15 mg/kg) at 20.00 on DII blocked ovulation in all of 8 and 7 rats, respectively, but these treatments did not block vaginal cornification at the expected time in any animal. (4) Administration of L-DOPA (100 mg/kg) or dihydroxy-phenylserine (DOPS, 200 mg/kg) with alpha-MPT (200 mg/kg) at 20.00 on DII reversed the blocking effect of alpha-MPT on ovulation in 3 out of 6 and 3 out of 5 rats, respectively. (5) Direct application of crystalline alpha-MPT or FLA-63 (about 3-5 mug) to the 3rd ventricle at 20.00 on DII also blocked ovulation in all of 7 and 5 rats, respectively. (6) Both systemic and intraventricular injections of alpha-MPT at 10.00 on DII reduced serum LH on P but not serum FSH. FLA-63 by intraventricular injection also reduced serum LH but not serum FSH. (7) Injection of 17beta-estradiol (40 mug s.c.) with alpha-MPT or FLA-63 partially removed the ovulatory blockade induced by conditions 1, 2, 3 and 5. Therefore, norepinephrine seems to be an important neurotransmitter in the release of gonadotropin responsible for estrogen secretion before P, but dopamine may also be involved during its early stage as represented by 10.00 on DII.

Serum progesterone and corpus luteum function in pregnant pigtailed monkeys (Macaca nemestrina)

Corpus luteum (CL) function and control during pregnancy and early lactation in the pigtailed macaque was investigated. Peripheral concentrations of progesterone (P) on day 10 of pregnancy were 12.98 +/- 2.21 ng/ml and decreased progressively to 7.96 +/- 1.27 ng/ml by day 21 of pregnancy. The concentration of P increased around day 27 of gestation and reached peak levels of 18.48 +/- 2.45 ng/ml on day 37, thereafter gradually decreasing to a nadir at about midgestation. Ten days before parturition P concentrations increased again (P < 0.05). Concentrations of P decreased from 6.62 +/- 1.48 ng/ml on the day of delivery to 2.16 +/- 0.43 ng/ml on day 2 of lactation and remained low thereafter. Ovariectomy on day 35 did not affect the normal course of gestation or the patterns of P secretion during pregnancy. However, in these ovariectomized animals, in spite of suckling, P was not detectable after parturition. In intact monkeys, serum concentrations of P in the utero-ovarian vein at days 80 and 159 of pregnancy were higher relative to the uterine vein. Incubation studies utilizing 3H-cholesterol as a substrate revealed that the CL were capable of synthesizing P on days 35 and 159 of gestation. Histologically, the CL contained active luteal cells at late pregnancy. Low serum concentrations of chorionic gonadotropin were detected on day 10 of gestation; concentrations of this hormone reached high levels between days 18 and 24 and the titers were nondetectable after day 40 of pregnancy. Luteinizing hormone was present in constant amounts in the circulation during pregnancy and lactation. These data suggest that the CL of pregnancy in the pigtailed monkey is functional or capable of functioning during various stages of pregnancy. However, the fetoplacental unit is the primary source of P during the latter 4.5 months of gestation. As in other primates, a functional CL is not required for maintenance of pregnancy after implantation nor for lactation. Thus, the physiological significance of CL function during pregnancy is unclear.

INCREASE IN FOLLICLE STIMULATING HORMONE CONTENT OCCURS IN CULTURED HUMAN FETAL PITUITARY CELLS EXPOSED TO GONADOTROPIN-RELEASING HORMONE

To investigate the mechanisms by which GnRH regulates FSH production in the human fetus, dispersed pituitary cells from second trimester human fetuses were cultured on surface-modified plates. Exposure of cells to GnRH [(10(-8) and 10(-7) mol/L), study I] or [D-Ala6]des-Gly10-GnRH ethylamide (DALA) [(10(-11) to 10(-7) mol/L), study II] for 48 h resulted in an elevation of total FSH which correlated with an increase in releasable, but not nonreleasable, FSH. When pituitary cells were incubated for 24, 48 and 72 h with and without 10(-8) mol/L GnRH (study III), total FSH was significantly increased in cells cultured for 48-72 h without GnRH compared to cells lysed at the beginning of the incubation (p less than 0.001). At all intervals, GnRH significantly enhanced total FSH compared to respective controls (p less than 0.05).