Regulation of thyrotropin secretion by the central epinephrine system. Studies in the chronically cannulated rat.
In the present investigation CNS epinephrine (EPI) biosynthesis was selectively interrupted with specific norepinephrine N-methyltransferase (NMT) inhibitors, SK&F 64139 (Smith, Kline & French Laboratories) and LY 78335 (Eli Lilly & Co. Research Laboratories), to determine the effects of central EPI depletion on basal and cold, thyrotropin-releasing hormone, and hypothalamic somatostatin antiserum induced thyrotropin (TSH) secretion in chronically cannulated rats. Because these NMT inhibitors also are alpha 2-adrenergic receptor blockers, the effects of alpha 2- and alpha 1-adrenergic blockade and alpha 2-activation on plasma TSH were assessed with rauwolscine and corynanthine and B-HT 933, respectively. Serum T4 and plasma corticosterone were also measured. Blockade of CNS EPI synthesis resulted in inhibition of basal and cold and thyrotropin-releasing hormone induced TSH release, suppression of serum T4, and increased corticosterone release. The stimulatory effect of SRIF antiserum on plasma TSH was not altered by SK&F 64139. alpha 2-adrenergic blockade suppressed plasma TSH levels, but not to the same degree as the NMT inhibitors; activation of alpha 2-receptors enhanced TSH secretion. Thus, it is possible that part of the effect of the NMT inhibitors on TSH was due to alpha 2-blockade. alpha 1-adrenergic blockade also lowered plasma TSH. These results indicate that central EPI systems have a stimulatory role in TSH regulation, possibly mediated by alpha 2-adrenergic receptors, cold-induced TSH release is mediated, in part, by EPI, and central EPI systems exert an inhibitory effect on the hypothalamic-pituitary-adrenal axis.
D000818:Animals; D001596:Benzylamines / Q000494:pharmacology; D002404:Catheterization; D004837:Epinephrine / Q000502:physiology*; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects / Q000502:physiology; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D010625:Phenylethanolamine N-Methyltransferase / Q000037:antagonists & inhibitors; D010913:Pituitary-Adrenal System / Q000187:drug effects / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology; D044005:Tetrahydroisoquinolines; D013972:Thyrotropin / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism
D001596:Benzylamines; D007546:Isoquinolines; D011942:Receptors, Adrenergic, alpha; D044005:Tetrahydroisoquinolines; C002569:2,3-dichloro-alpha-methylbenzylamine; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; C012153:7,8-dichloro-1,2,3,4-tetrahydroisoquinoline; D010625:Phenylethanolamine N-Methyltransferase; D004837:Epinephrine