A combined test of anterior pituitary reserve.
Determination of the functional reserve of the anterior pituitary gland requires the serial measurement of hormones released from the pituitary by specific stimuli. Individually, insulin-induced hypoglycaemia, thyrotrophin releasing hormone (TRH) and gonadotrophin releasing hormone (GnRH) have proved to be reliable stimuli for the release of the various pituary hormones. The maximum incremental hormone response of growth hormone, cortisol, luteinising hormone, follicle stimulating hormone, thyrotrophin, triiodothyronine and prolactin has been assessed after the simultaneous administration of insulin, TRH and GnRH in six normal subjects. These responses have been compared to previously determined responses in a normal population when insulin, TRH or GnRH have been given separately. There were no significant differences in the peak response or the maximum incremental response of any hormone. The test has been used to assess the pituitary reserve of 54 patients with disorders of the hypothalamic-pituitary axis, and five patients have been assessed both before and after hypophysectomy. The test is found to be convenient, sensitive and reliable in the assessment of pituitary reserve.