The effect of adrenoreceptor antagonists and agonists on LHRH release from the stalk-median eminence in the pig.
A release of radio-immunoassayable LHRH from the stalk-median eminence of neonatal piglets and prepubertal gilts was measured using an in vitro incubation system. The stalk-median eminence was collected from one-week-old male (n = 19) and female (n = 21) piglets and from 6-month-old prepubertal ovariectomized gilts given oestradiol benzoate (20 micrograms/kg b.w.; n = 52) or left untreated (control; n = 25) 30 or 68 h before slaughter. Each vial, containing the stalk-median eminence in 2 ml of Krebs-Ringer bicarbonate buffer, was incubated for 30 min, followed by 30 min incubations during which either basal release or the effect of adrenoreceptor antagonists and agonists on LHRH output was evaluated. There were no differences between the basal release of LHRH (x +/- SEM; pg/ml) from the stalk-median eminence of male (65.5 +/- 9.8) and female (66.3 +/- 9.6) newborn piglets. The addition of propranolol (10(-6) M) caused a 250% increase in LHRH release from the stalk-median eminence explants of neonatal males (p = 0.08) and females (p < 0.05). Neither norepinephrine nor phentolamine affected LHRH release from the stalk-median eminence of newborn males and females. The basal release of LHRH (pg/ml) from the stalk-median eminence explants collected from ovariectomized gilts given oestradiol benzoate 30 and 68 h before slaughter or left untreated was similar (147.5 +/- 36.1, 236.4 +/- 77.7 and 202.0 +/- 41.6, respectively). Propranolol evoked a significant increase in LHRH secretion from the stalk-median eminence in the control group, but not in the groups given oestradiol benzoate. Norepinephrine (10(-6) M) increased LHRH release from the stalk-median eminence collected from the control animals, 30 h and 68 h after oestradiol benzoate treatment by 48, 78 and 73 percent, respectively. Phentolamine (10(-6) M) did not affect LHRH release from the stalk-median eminence in control animals and ovariectomized gilts primed with oestradiol benzoate. Urapidil (10(-6) M, alpha 1-adrenoreceptor antagonist) did not affect the basal LHRH release from the stalk-median eminence of gilts from the control group and group slaughtered 30 h after oestradiol benzoate treatment, but caused a rapid increase of LHRH release from the stalk-median eminence 68 h after oestradiol benzoate treatment. Phenylephrine (10(-6) M) did not affect LHRH output from the stalk-median eminence collected at various time periods after oestradiol benzoate administration in vivo. These results suggest that in pigs, nerve terminals releasing LHRH at the stalk-median eminence level are sensitive to adrenergic stimulation or inhibition and that the adrenergic system can be modulated by estrogens in the prepubertal gilts.
Wasowicz
G
G
Division of Reproductive Endocrinology and Pathophysiology, Polish Academy of Sciences, Olsztyn, Poland.
Elsaesser
F
F
Ziecik
A J
AJ
D000322:Adrenergic Agonists / Q000494:pharmacology*; D018674:Adrenergic Antagonists / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008473:Median Eminence / Q000187:drug effects* / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010052:Ovariectomy; D010646:Phentolamine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D013552:Swine
D000322:Adrenergic Agonists; D018674:Adrenergic Antagonists; D010879:Piperazines; C074283:estradiol 3-benzoate; D010656:Phenylephrine; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D011433:Propranolol; C015568:urapidil; D011188:Potassium; D009638:Norepinephrine; D010646:Phentolamine