Regulation of alpha-melanocyte-stimulating hormone secretion from the pars intermedia of domestic cats.
OBJECTIVE
To identify factors regulating secretion of alpha-melanocyte-stimulating hormone (alpha-MSH) from the pars intermedia (PI) of the pituitary gland of cats.


METHODS
28 healthy adult cats.


METHODS
Indwelling catheters were placed in 1 jugular vein of each of 7 to 10 cats, depending on treatment group. Sixteen hours later, 3 blood samples were collected for determination of baseline plasma hormone concentrations, and saline solution or a test substance (haloperidol, corticotropin-releasing hormone, bromocriptine, isoproterenol, insulin, or dexamethasone) was administered via the catheter. Subsequent blood samples were collected at regular intervals for up to 240 minutes after injection. Concentrations of ACTH, cortisol, and alpha-MSH were measured in plasma by use of specific radioimmunoassays. Cats were rested for at least 3 weeks between experiments.


RESULTS
Administration of haloperidol and isoproterenol resulted in increased, and bromocriptine and insulin in decreased, circulating concentrations of alpha-MSH from baseline. ACTH and plasma cortisol concentrations increased after administration of all test substances except dexamethasone. Dexamethasone injection resulted in decreased plasma concentrations of ACTH and cortisol.


CONCLUSIONS
Secretion of alpha-MSH from the PI of cats appears to be inhibited by dopaminergic activity and stimulated by beta-adrenergic influences. Activation of secretion of alpha-MSH from the PI can be dissociated from activation of secretion of other pro-opiomelanocortin-derived peptides, such as ACTH, arising from the pars distalis. Regulation of secretory activity of the PI of cats resembles that of rats.
Department of Anatomy, Physiology, and Pharmacology, College of Veterinary Medicine, Auburn University, AL 36849, USA.
R J
RJ
Kemppainen
M E
ME
Peterson
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000324:Adrenocorticotropic Hormone / Q000097:blood; D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology; D002415:Cats / Q000502:physiology*; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D005260:Female; D005938:Glucocorticoids / Q000494:pharmacology; D006220:Haloperidol / Q000494:pharmacology; D006854:Hydrocortisone / Q000097:blood; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000097:blood / Q000378:metabolism*; D010902:Pituitary Gland / Q000378:metabolism*; D011863:Radioimmunoassay / Q000662:veterinary
D000318:Adrenergic beta-Agonists; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D005938:Glucocorticoids; D007004:Hypoglycemic Agents; D007328:Insulin; D001971:Bromocriptine; D003907:Dexamethasone; D000324:Adrenocorticotropic Hormone; D009074:Melanocyte-Stimulating Hormones; D003346:Corticotropin-Releasing Hormone; D006220:Haloperidol; D007545:Isoproterenol; D006854:Hydrocortisone