Effect of alpha-methyl-p-tyrosine and an antiserum to rat growth hormone (GH)-releasing factor (GRF) on plasma GH secretory profile during a continuous infusion of human GRF in rats.
The effects of alpha-methyl-p-tyrosine (alpha-MT) and an antiserum specific to rat growth hormone-releasing factor (GRF) on growth hormone (GH) secretory profile during a 6-h continuous infusion of human GRF(1-44) NH2 were observed in unrestrained adult male Wistar rats. All rats were provided with two indwelling cannulae; one in the right atrium for undisturbed blood collection and the other in the inferior vena cava for 0.9% NaCl or GRF infusion. GRF was administered by an infusion pump at a dose of 50 ng/kg b.wt./min ma GH levels during baseline period were low with little fluctuation. GH secretion was augmented significantly during continuous GRF infusion in control rats but interpeak intervals remained unaltered. When an antiserum specific to rat GRF was administered, episodic GH secretion was abolished. In these rats, pulsatile GH secretion indistinguishable from that of control rats was observed in the continuous presence of human GRF. Although alpha-MT inhibited episodic GH secretion, alpha-MT-treated rats exhibited high-frequency, low-amplitude episodic GH secretion and elevated baseline levels during the stimulation. There were no differences in the amount of GH secreted during GRF infusion between rats that had received either alpha-MT or antiserum to rat GRF. Since GH secretion to GRF is determined largely by somatostatin, the results suggest that phasic release of somatostatin plays an important role in determining the rhythmicity of episodic GH secretion, and that it is modulated by alpha-MT but not by the immunoneutralization of GRF.
Sugihara
H
H
Department of Medicine, Nippon Medical School, Tokyo, Japan.
Wakabayashi
I
I
Minami
S
S
Takahashi
F
F
Shibasaki
T
T
Ling
N
N
D000818:Animals; D013006:Growth Hormone / Q000097:blood*; D013007:Growth Hormone-Releasing Hormone / Q000276:immunology / Q000494:pharmacology*; D006801:Humans; D007106:Immune Sera / Q000494:pharmacology*; D008297:Male; D008781:Methyltyrosines / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D019805:alpha-Methyltyrosine
D007106:Immune Sera; D008781:Methyltyrosines; D019805:alpha-Methyltyrosine; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone