Combined pituitary stimulation test: interactions of hypothalamic releasing hormones in man

The use of hypothalamic releasing hormones for the clinical assessment of anterior pituitary function is both simple and free of severe side effects. Tests with the recently discovered substances GRF and CRF as well as with combinations of several releasing hormones are therefore used in many clinics. A reliable interpretation of such combined tests, however, is only possible when positive or negative interactions between these releasing hormones are known. After a rest of 2 h to reach basal cortisol levels, 7 groups of 5 male volunteers each received an iv bolus injection consisting of either: A): GRF (100 micrograms) + CRF (50 micrograms) + TRH (200 micrograms) + LHRH (100 micrograms), B): CRF + TRH, C): GRF + TRH, D): LHRH + TRH, E): TRH, F): GRF, G): CRF. During the following 2 h, GH, TSH, cortisol, LH, FSH and prolactin were measured every 15 min. The TSH response after the injection of all 4 releasing hormones was significantly higher (delta TSH = 16.5 +/- 2.0 microU/ml, x +/- SE) compared to the injection of TRH alone (delta TSH = 9.3 +/- 1.4 microU/ml; p less than 0.025). This increment in TSH secretion was confirmed when 2 groups of 5 female volunteers were studied with the TRH-test (delta TSH = 9.9 +/- 1.8 microU/ml) or the combination of all four releasing hormones (delta TSH = 16.8 +/- 2.9 microU/ml; p less than 0.05). This exaggerated TSH-response to TRH was demonstrated to be entirely due to simultaneous administration of GRF, whereas CRF and LHRH in combination with TRH had no additional effect on TSH release.(ABSTRACT TRUNCATED AT 250 WORDS)