Induction of Cellular Follicle-Stimulating Hormone in the Hamster Adenohypophysis Requires Intermittent Stimulation by Luteinizing Hormone Releasing Hormone

We investigated the effectiveness of continuous vs intermittent LHRH stimulation of the neonatal female anterior pituitary gland on inducing cellular FSH immunoreactivity in the Golden Syrian hamster. Neonatal female pituitary glands were grafted beneath the right renal capsules of hypophysectomized-ovariectomized adult hosts with a catheter implanted in the external jugular vein. In experiment 1, vehicle or LHRH (6 ng/h) was infused continuously or LHRH was pulsed at 1 h (6 ng) or 12 h (72 ng) intervals through the catheters for 8 days. Hamsters were decapitated for collection of trunk blood shortly after the end of treatment, and grafts were prepared for immunocytochemical staining for LH and FSH. Anterior pituitary glands removed from neonatal (day 1) and day 9 female pups also were stained for LH and FSH. The mean percentage of adenohypophysial cells staining for LH increased from 11% in neonatal pups to mean percentages (24-28%) that were similar in day 9 pups and in all groups with grafts. The mean percentage of adenohypophysial cells staining for FSH increased from 1% in neonatal pups to percentages (16–21%) that were similar in day 9 pups and in grafts in hosts administered 6 or 72 ng LHRH pulses. By contrast, the mean percentage of FSH cells did not increase in grafts in hosts administered vehicle or LHRH by continuous infusion. Serum LH concentration was low in hosts given vehicle or LHRH by continuous infusion but elevated in hosts given 72 ng LHRH pulses and in all but one host given 6 ng LHRH pulses. Serum FSH concentration was detectable in some of the hosts given 6 or 72 ng LHRH pulses and non-detectable in the rest of the hosts. In experiment 2, the mean percentage of adenohypophysial cells staining for FSH did not increase in grafts in hosts infused with LHRH continuously at 72 ng/h compared to that observed in hosts pulsed with vehicle every h for 8 days (1.4 vs 2.0%). The data demonstrate that intermittent but not continuous stimulation of neonatal female adenohypophysial cells by LHRH is effective in inducing cellular FSH immunoreactivity. The data also strongly suggest that LHRH release is episodic during the first week after birth in the female hamster. To our knowledge, these results are the first to provide evidence suggesting that the episodic LHRH release system is functioning to exert an important biological effect in a neonatal mammal and that the mechanism for down-regulation of LHRH receptors in gonadotrophs can be activated this early in life.