Pulsatile Secretion of Luteinizing Hormone during the Menstrual Cycle of Rhesus Macaques*

Abstract

The secretion of LH, PRL, and cortisol was investigated in 4 sexually mature female rhesus macaques with cardiac catheters protected by tethers. Based on endocrine parameters, all 4 of the animals ovulated within 2 months from the time they were tethered, and regular menstrual cycles of 24-34 days were observed. The catheters remained patent for 6-12 months without reposition or repair. Plasma levels of 2 stress-labile hormones, PRL and cortisol, showed diurnal fluctuations comparable to those observed in untethered animals. The frequency of LH secretory episodes was determined by measuring bioactive LH in blood samples collected at 10-min intervals in the follicular phase and at 15-min intervals in the luteal phase of the menstrual cycle. In 10 trials during the follicular phase, we estimated that an average of between 14 and 15 LH pulses occurred every 12 h. The interpulse interval ranged between 20-80 min and averaged 50 min. No change in pulse frequency was observed across the follicular phase. The number of LH pulses decreased after ovulation, and by the end of the luteal phase, the interpulse interval was 4-6 h. One example during the preovulatory LH surge revealed the high frequency, high amplitude nature of LH secretion at that time. Our experience indicates that tethered animals with cardiac catheters show no hormonal indications of stress and represent the best available model for studies requiring frequent and prolonged access to the vascular system. Our data suggest that peripheral LH fluctuations in rhesus monkeys, as in other mammals, are pulsatile, and the frequency of these pulsatile episodes changes with different phases of the menstrual cycle, presumedly in response to varying stimuli to the pituitary from the brain.

Effects of hyperandrogenemia and increased adiposity on reproductive and metabolic parameters in young adult female monkeys

“…Open bars, controls. *Significant difference between groups, P ϭ 0.02; †significant difference from before WSD, P Ͻ 0.05; #trend toward difference from before WSD, P ϭ 0.062. ular phase (38,64). Thus, it appears that, although T treatment led to an earlier activation of the LH pulse generator in monkeys (59), this difference was not maintained as monkeys matured into adulthood, and was not exacerbated by consuming a WSD.…”

Unexpected responses of the hypothalamic gonadotropin-releasing hormone "pulse generator" to physiological estradiol inputs in the absence of the ovary.

“…Furthermore, the rising tide of estrogen during the f llicular phase of the cycle is not accompanied by a reduct on in LH pulse frequency. On the contrary, it has been s ggested that the time of the initiation of the preovulatory g nadotropin surge may be associated with a small increase i the frequency of LH secretory episodes (3)(4)(5)(6)8). These servations dictate the conclusion that estrogens have little cr no effect on the modulation of LH pulse frequency, in ontrast to progesterone, which unambiguously decelerates t ie pulsatile release of this gonadotropic hormone (1-6, 8, 10, 1).…”

“…tiHely constant in the face of widely varying levels of estradiol ( 2) in the peripheral circulation-e.g., in the course of the f Ilicular phase of the menstrual cycle and after ovariectomy. MATERIALS he frequency of luteinizing hormone (LH) pulses during the f llicular phase of the menstrual cycle in women (1-6) and rhesus monkeys (7,8) does not appear to differ from that o served in the total absence of ovarian estrogen secretion ( 2, 9). Furthermore, the rising tide of estrogen during the f llicular phase of the cycle is not accompanied by a reduct on in LH pulse frequency.…”

Ovarian Regulation of Pulsatile Luteinizing Hormone Secretion During Late Gestation in the Rat*

“…Inhibin activity in ovarian venous plasma also increases significantly at the end of gestation in the rat (12). Thus, in addition to the ovarian steroidinduced restraint on LH pulse amplitude between Days 21 and 22 of gestation, other ovarian factors found in follicular fluid may be the follicular phase of the menstrual cycle in the ovary-intact animal (32,33) and in the OVX monkey in the absence of ovarian E, (34). However, Knobil and colleagues (27) have shown that physiological follicular phase plasma levels of E, markedly reduced or completely inhibited the frequency of LH pulses in OVX monkeys.…”