Hypothalamus and endocrine function in persistent estrous rats at low environmental temperature

¹ Daniel Baugh Institute of Anatomy, Jefferson Medical College, Philadelphia, Pennsylvania

Persistent vaginal estrus with uterine and pituitary hypertrophy were found in adult female rats 4–10 months after placement of preoptic and anterior hypothalamic lesions. Serum TSH, I¹³¹ release rate and histology of the thyroid and ascorbic acid concentration of adenohypophysis, ovary and adrenal were normal. Exposure of lesioned rats to cold (5°C, 36–55 days) profoundly altered pituitary-target gland functions. Ovarian atrophy and uterine involution resulted; vaginal cornification ceased. Pituitary hypertrophy was inhibited but ascorbic acid concentration was maintained. Serum and pituitary TSH levels decreased and acceleration of thyroidal radioiodine release was prevented. Apparent dichotomy in adrenal responses developed. Despite enlarged adrenals, plasma corticosterone level in cold stressed, operated rats averaged less than one-third that of intact controls. Adrenal ascorbic acid concentration remained normal. The results underscore the basic role of central nervous mechanisms in endocrine function under chronic cold stress. Hypothalamic lesions which permit adequate trophic hormone secretion at normal temperatures drastically curtail thyroidal and ovarian function and selectively limit adrenal responses in the cold.