Growth hormone releasing activity of thyrotropin-releasing hormone in rats with hypothalamic lesions.
The growth hormone (GH)-releasing effect of thyrotropin-releasing hormone (TRH) was investigated in rats in which central nervous system (CNS)-anterior pituitary (AP) connections had been experimentally interrupted. Sprague-Dawley (SD) female and male rats, underwent bilateral electrolytic lesions in the median eminence (ME) or the ventromedial nuclei (VMN) or were sham-operated (sham-op). Fifteen days after surgery, 0.9% NAACl or TRH was injected iv into sham-op rats or those with lesions in the CNS, anesthetized with urethane, and blood was drawn at 5 and 10 min posttreatment. In the rats with ME lesions, TRH at all the doses used (0.1, 0.4 and 0.8 microng/100 g BW) induced a marked, although not dose-related GH rise, which was not present in sham-op rats after TRH, or after NaCl administration to either rats with ME lesions or sham-op rats. In SD male rats lesioned in the VMN, TRH at doses of 0.4 and 0.8 microng/100 g BW induced significant GH rises, while the lowest TRH dose (0.1 microng/100 g BW) was ineffective; again, TRH was ineffective at all doses used in sham-op rats. Concomitant evaluation of the prolactin (PRL)-releasing effect of TRH (0.1-0.8 microng/100 g BW), showed a striking elevation of plasma PRL in both female and male sham-op controls, but no PRL rise in the rats with ME lesions. The results reveal that in the rat with surgical separation of the anterior pituitary from the CNS, a direct GH-releasing effect of TRH can be obtained, whereas its PRL-releasing effect is no longer observed, and suggest that, by analogy, the GH-releasing effect of TRH present in some disease states of the human may be due to an impairment of CNS-AP connections.
D000818:Animals; D002746:Chlorpromazine / Q000494:pharmacology; D005260:Female; D013006:Growth Hormone / Q000097:blood; D013007:Growth Hormone-Releasing Hormone / Q000502:physiology*; D007031:Hypothalamus / Q000502:physiology*; D008297:Male; D008473:Median Eminence / Q000502:physiology; D010903:Pituitary Gland, Anterior / Q000033:anatomy & histology / Q000378:metabolism; D011388:Prolactin / Q000097:blood; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D002746:Chlorpromazine