Circhoral Fluctuations of Serum Total Renin, Inhibin and Related Hormones Around the Mid-cycle in Normal Human Females

Total renin and inhibin are secreted by the ovary. Although luteinizing hormone (LH) and/or follicle stimulating hormone (FSH) may stimulate their secretion, the close relationship between fluctuations of gonadotrophins, oestradiol, progesterone, renin and inhibin during the cycle is still conjectural. Tc investigate the temporal relationship between the short-term fluctuations in the circulating concentrations of LH and FSH and the ovarian hormones (oestradiol, progesterone, renin and inhibin), blood samples were collected at 15-min intervals for 6 h from 15 normal women in the late follicular (n = 4), early luteal (n = 5) or luteal (n = 6) phases of the menstrual cycle. LH levels showed the well-known pulsatile secretion with decreasing frequency and increasing relative amplitude from the late follicular to the luteal phase. Progesterone and oestradiol serum levels were pulsatile, 25% and 35-50% of which were linked to LH pulses, with time lags of 30 and 12-15 min respectively. Renin levels presented significant pulses, 26% of which were related to LH pulses with a time lag of < 10 min; no coincidence was found between renin and oestradiol pulses. Inhibin levels presented only scattered pulses of small amplitude, which were unrelated to LH or FSH. These results show that, besides the LH-related pulses, pulsatile secretion of some ovarian hormones (oestradiol, progesterone and renin) may also occur independently of LH pulses and may be unrelated to one another. Moreover, contrary to the other ovarian hormones, inhibin seems to follow a tonic, not a pulsatile type of secretion around the mid-cycle.