ABSTRACT
Michael Nilsson Institute of Neurobiology, Sahlgrenska University Hospital, Goteborg, Sweden
Lawrence A. Frohman and Rhonda D. Kineman University of Illinois at Chicago, Chicago, Illinois
I. REGULATION OF PULSATILE GH SECRETION
In rodents, and maybe also in other species. episodic growth hormone (GH) secretion is important for several biological functions. These include sexual dimorphism of the liver (1,2) but, possibly, also functions of other organs (3). Studies in male rats have indicated that pulsatile GH secretion (4) is regulated at the pituitary level by an interplay between reciprocal and rhythmic release of GH-releasing hormone (GHRH) and somatostatin from the hypothalamus. Thus, each GH pulse is accompanied by increased release of GHRH and decreased release of somatostatin (5,6). At the hypothalamic level, there appears to be crosstalk between GHRH and somatostatin-containing neurons. Somatostatin appears to inhibit GHRH release (6), and GHRH may stimulate somatostatin release (7). It was shown by Clark and Robinson (8) that intravenous (iv) infusions of GHRH pulses at 3-h intervals to female rats, which normally have a more continuous GH secretory pattern than male rats (2), induce a male-type plasma GH pattern, with GH pulses following each GHRH infusion and, per-
406 Jansson et al.
