EFFECT OF SUBSTANCE-P ON BASAL AND THYROTROPIN-RELEASING HORMONE-STIMULATED THYROTROPIN RELEASE IN HUMANS

To test the possible effects of intravenous administration of substanc e P (SP) on basal and thyrotropin-releasing hormone (TRH)-stimulated t hyrotropin (TSH) release, SP was infused alone (0.5 or 1.5 pmol/kg(-1) /min(-1) for 60 minutes) or after TRH (20 or 400 mu g in an intravenou s bolus) in 21 normal male subjects (aged 26 to 36 years) and in 18 no rmal women (aged 25 to 32 years). Women were studied during follicular (day 6 to 8) and luteal (day 21 to 23) phases of following regular me nstrual cycles. In addition, plasma cortisol levels during SP infusion were measured. In agreement with previous findings, significant incre ments in plasma cortisol levels were observed in men and women when th e higher (1.5 pmol/kg(-1)/min(-1)) but not the lower (0.5 pmol/kg(-1)/ min(-1)) amount of SP was administered. In contrast, in both men and w omen basal and TRH (20 or 400 mg)-induced TSH releases were not modifi ed by SP at any tested amount. Results in the follicular and luteal ph ase were similar. These data suggest that in normal men and women plas ma SP is not involved in the control of TSH release, at least not outs ide the blood-brain barrier. Copyright (C) 1995 by W.B. Saunders Compa ny