Continuous infusion of a gonadotrophin-releasing hormone (GnRH) agonist (buserelin) by osmotic minipump from day 1 of the luteal phase in five Welsh ewes resulted in a sustained suppression of plasma concentrations of FSH which increased three- to eightfold within 2 days after the end of infusion 29 days later. Plasma concentrations of LH increased three- to eightfold over the first 5 days of infusion and then became basal and non-pulsatile until 1 day after the end of infusion. Duration of the luteal phase and plasma concentrations of progesterone were not significantly different in control and treated ewes. Pulses of LH in control ewes were followed by increases in concentrations of progesterone in samples collected at 10-min intervals for 7 h on days 10 and 14 of the luteal phase. However, progesterone was also released in a pulsatile manner in the absence of LH pulses in both control and GnRH agonist-treated ewes. After natural luteolysis, no ovulation or corpus luteum function occurred in treated ewes up to 15 days after the end of treatment on day 29, even though oestrus, indicating follicular development and oestrogen secretion, had occurred 8-11 days after treatment ended. After 30 days of infusion the ovaries of GnRH agonist-treated ewes contained no follicles greater than 2.5 mm in diameter. In follicles of 1-2 mm in diameter the basal and LH-stimulated production of oestradiol and testosterone in vitro were similar in both control and GnRH agonist-treated ewes, and a similar proportion of these follicles was oestrogenic (greater than 370 mol oestradiol per follicle) in GnRH agonist-treated and control ewes. These results show (1) that progesterone secretion by the corpus luteum of the ewe can be sustained in the presence of basal concentrations but absence of pulsatile secretion of LH, and progesterone is released in a pulsatile manner whether or not LH pulses are present, (2) that follicular development beyond 2.5 mm in diameter in the ewe is dependent upon adequate stimulation by both LH and FSH and (3) that the continuous infusion of GnRH agonist is a simple method for providing reproducible suppression of LH and FSH and follicular development in the ewe to allow the study of gonadotrophin action on the ovary in vivo.

The biosynthesis of oestrogens from androgens is catalysed by the aromatase complex, an essential component of which is the aromatase cytochrome P450 (P450 arom) protein. Expression of a functional P450 arom is essential for normal fertility in males and females and the sequence of the protein is highly conserved. We have raised a new monoclonal antibody against a conserved peptide and validated it on fixed tissue sections of the rat, common marmoset (Callthrix jacchus) and human. The monoclonal antibody was used successfully for Western analysis and specifically reacted with a 55 kDa protein in microsomal extracts. On sections of ovaries in all three species, expression in follicles was specific to the mural granulosa cells of antral follicles and was present in corpora lutea. In the human and marmoset, staining of luteal cells was markedly heterogeneous and did not appear to vary consistently with the stage of the cycle. The intensity of immunostaining was elevated in corpora lutea from pregnant rats and following human chorionic gonadotropin rescue in the human. In the testis, the highest levels of expression were observed in the Leydig cells within the interstitium. In adult rat and marmoset, and possibly also in the human, some P450 arom was associated with the cytoplasm surrounding elongate spermatids but other germ cells were immunonegative.In conclusion, a new monoclonal antibody specific for P450 arom recognises the protein in rodent, primate and human. Its ability to work on fixed tissue sections will facilitate identification of individual cells expressing P450 arom within complex tissues.

Active immunization of 6 Damline ewes against LHRH during seasonal anoestrus resulted in an inhibition of ovarian cyclicity throughout 2 subsequent breeding seasons. This was associated with a significant suppression of plasma LH and FSH concentrations but no significant effect on prolactin. The ovaries of LHRH-immunized ewes 30 months after primary immunization contained no follicles greater than 2.5 mm in diameter and a greater proportion of follicles between 1 and 2 mm were atretic than in control ewes (N = 8). In-vitro production of testosterone and androstenedione were similar in follicles 1-2 mm in both control and LHRH-immunized ewes (N = 6) and all had little or no ability to secrete oestradiol. However, basal and hCG-stimulated progesterone secretion was suppressed in the follicles from LHRH-immunized ewes. These results show that follicular development beyond 2.5 mm in the ewe is dependent on adequate stimulation by both LH and FSH.

It appears from the evidence documented in this Commentary that the neonatal period is another critical stage in the process of sexual, behavioural and immune system development and maturation in primates. Interference with normal brain-pituitary-gonadal function during this period (e.g. with a GnRH analogue in monkeys) appears to impact adversely on subsequent reproductive, immunological and behavioural function. These data further emphasize the importance of fully understanding the regulatory mechanisms that govern neonatal gonadal function in the primate, if we are to eliminate, control or minimize the potential risk resulting from its disruption in humans. Given the recent evidence that the reproductive potential of the human male has declined rather dramatically over the last 50 years, and that clinical conditions associated with abnormal testicular function are on the rise, continued investigation in this area would appear to be imperative.

The role of the pituitary gonadotrophins in controlling luteal function in the stumptailed macaque has been investigated by examining profiles of serum concentrations of LH, FSH, progesterone and oestradiol in daily blood samples from 13 monkeys during the menstrual cycle, and in blood samples taken at hourly intervals between 09.00 and 21.00 h on different days of the luteal phase in 13 cycles. The effects of acute withdrawal of gonadotrophins was investigated by administering a single injection of 300 micrograms LHRH antagonist/kg body weight at different stages of the luteal phase during 28 cycles. Although there were high basal values and marked fluctuations of bioactive LH during the first 4 days after the LH peak, progesterone profiles showed no corresponding short-term changes, there being a slow and steady rise in progesterone concentrations during the sampling periods. After day 5, basal LH secretion decreased, but high amplitude LH pulses were identified which were associated with episodes of progesterone secretion. Administration of the LHRH antagonist caused a suppression of bioactive LH and progesterone concentrations at all stages of the luteal phase, although some basal secretion of progesterone was maintained through the 24-h period of effective antagonist gonadotroph blockade. Luteal function recovered apparently normally in all monkeys treated in the early-mid-luteal phase. Serum concentrations of FSH and oestradiol fluctuated comparatively less during the 12-h sampling periods, and the antagonist had less suppressive effects on the concentrations of these hormones. The LHRH antagonist had no apparent effect on prolactin release.(ABSTRACT TRUNCATED AT 250 WORDS)