PARTIAL SYNCHRONY OF THE OESTROUS CYCLES OF RATS INTRODUCED TO A NEW ENVIRONMENT

Abstract

Carbonic anhydrase (CA) and Mg²⁺-dependent ATPase and Mg²⁺-dependent, HCO₃⁻-dependent ATPase (Mg²⁺-HCO₃⁻-ATPase) activities in rat duodenal mucosa and kidney cortex were examined with respect to thyroidal status. Administration of 50 and 150 μg thyroxine (T₄)/kg per day s.c. for 7 days decreased duodenal cytosol CA activity to 66% of control with the former and 43% with the latter dose, while Mg²⁺-HCO₃⁻-ATPase activity in brush borders of duodenal mucosa was increased to 116% of control by 150 μg T₄/kg. CA and Mg²⁺-HCO₃⁻-ATPase activities in the cytosol and brush border of kidney cortex did not change after administration of T₄. Hypothyroidism induced by thyroidectomy for 2 and 4 weeks or administration of methimazole (2·5–20 mg/kg per day s.c. or peroral) for 2, 3 and 4 weeks all increased duodenal cytosol CA activity, to about 140% at 2 weeks and 153% at 4 weeks after thyroidectomy, and to about 136% after the oral administration of 10 mg methimazole/kg per day for 4 weeks, while brush border Mg²⁺-HCO₃⁻-ATPase activity was decreased to 56% of control 4 weeks after thyroidectomy and to 74% after the s.c. administration of 20 mg methimazole/kg per day for 3 weeks. The increase in CA activity and the decrease in ATPase activity after thyroidectomy were restored to normal levels by replacement with T₄. Neither enzyme activity in the kidney changed in hypothyroidism. Serum concentrations of T₄ and cortisol-like material increased after administration of T₄, and serum concentrations of T₄, aldosterone and cortisol-like material all decreased in hypothyroidism. Correlations were observed between duodenal CA and Mg²⁺-HCO₃⁻-ATPase activities and serum concentrations of T₄ (P < 0·01). These results reveal that the decrease in CA activity and the increase in Mg²⁺-HCO₃⁻-ATPase activity of duodenal mucosa in hyperthyroidism are reversed in hypothyroidism, while both enzyme activities in the kidney are unrelated to thyroidal status. Journal of Endocrinology (1990) 126, 119–129