The binding of 3H-(3-MeHis2) thyrotropin releasing hormone to brain membranes and temperature response to thyrotropin releasing hormone in different strains of mice.

The effect of thyrotropin releasing hormone (TRH) on the colonic temperature of five strains of mice, namely, Swiss Webster, ICR, C57 BL, BALB and DBA, was determined. Intraperitoneal injection of TRH induced an hyperthermic response, the magnitude of which differed in different strains of mice. Peak effect was observed 15 min after the injection and the effect lasted for about an hour depending upon the dose. TRH produced a dose related hyperthermia in DBA mice, whereas in other strains an inverted U-shaped curve was obtained, with maximal response at 20 mg/kg and declining at 40 mg/kg dose. 3H-(3-Mehis2) TRH bound specifically to brain membranes at a single high affinity site with a B max of 53.72 fmol/mg protein, and Kd of 3.77 nM (for swiss Webster mice). The Kd and B max values did not differ for any strain. It is concluded that the nature of TRH induced changes in colonic temperature depends both on the dose and the strain of mice, and that factors other than the brain receptors for TRH may be responsible for its variable hyperthermic effect.