ASSESSMENT OF A COMBINED ANTERIOR-PITUITARY FUNCTION-TEST IN BEAGLE DOGS - RAPID SEQUENTIAL INTRAVENOUS ADMINISTRATION OF 4 HYPOTHALAMIC RELEASING HORMONES

A combined anterior pituitary (CAP) function test was assessed in eigh t healthy male beagle dogs. The CAP test consisted of sequential 30-se cond intravenous administrations of four hypothalamic releasing hormon es in the following order and doses: 1 mu g of corticotropin-releasing hormone (CRH)/kg, 1 mu g of growth hormone-releasing hormone (GHRH)/k g, 10 mu g of gonadotropin-releasing hormone (GnRH)/kg, and 10 mu g of thyrotropin-releasing hormone (TRH)/kg. Plasma samples were assayed f or adrenocorticotropin, cortisol, GH, luteinizing hormone (LH), and pr olactin (PRL) at multiple times for 120 min after injection. Each rele asing hormone was also administered separately in the same dose to the same eight dogs in order to investigate any interactions between the releasing hormones in the combined function test. Compared with separa te administration, the combined administration of these four hypothala mic releasing hormones caused no apparent inhibition or synergism with respect to the responses to CRH, GHRH, and TRH. The combined administ ration of these four hypothalamic releasing hormones caused a 50% atte nuation in LH response compared with the LH response to single GnRH ad ministration. The side effects of the combined test were confined to r estlessness and nausea in three dogs, which disappeared within minutes after the administration of the releasing hormones. It is concluded t hat with the rapid sequential administration of four hypothalamic rele asing hormones (CRH, GHRH, GnRH, and TRH), the adenohypophyseal respon ses are similar to those occurring with the single administration of t hese secretagogues, with the exception of the LH response, which is lo wer in the CAP test than after single GnRH administration.