THYROID-STIMULATING HORMONE RESPONSES AFTER SINGLE ADMINISTRATION OF THYROTROPIN-RELEASING-HORMONE AND COMBINED ADMINISTRATION OF 4 HYPOTHALAMIC RELEASING HORMONES IN BEAGLE DOGS

Thyrotropin (TSH) responses were determined in eight healthy male beag le dogs after a single administration of thyrotropin-releasing hormone (TRH) and the combined administration of four hypothalamic releasing hormones, i.e., corticotropin-releasing hormone, growth hormone-releas ing hormone, gonadotropin-releasing hormone, and TRH. In both tests, T RH was administered in a dose of 10 mu g/kg. Basal TSH concentrations ranged form 0.07 to 0.27 mu g/l (mean +/- SE, 0.14 +/- 0.02 mu g/l). T he administration of TRH, alone or in the combined test, resulted in a prompt and significant increase in TSH with mean (+/-SE) plasma TSH p eaks of 1.26 +/- 0.22 mu g/l at 10 min and 0.85 +/- 0.17 mu g/l at 30 min, respectively. The area under the curve (0-120 min) was significan tly lower in the combined test than in the single TRH test, whereas th e increments were not significantly different. It is concluded that me asurements of TSH responses to TRH alone and in combination with other releasing hormones can be used for the assessment of pituitary thyrot ropic cell function. In the combined test, the TSH response is slightl y lower than that in the single test.