Further studies on the regulation of the Harderian glands of golden hamsters by the thyroid gland.

Long-term increased or decreased circulating levels of thyroid hormones significantly modify porphyrin concentrations and morphology in the Harderian glands of male and female hamsters. Administration of T3 reduced porphyrin concentrations in females; this treatment or decreasing thyroid hormone levels with KClO4 suppressed the post-castration rise of porphyrins in males. Hypophysectomy led to increased porphyrins in the Harderian glands of males; this rise was suppressed in hypophysectomized males by T3 or T4. In females, hypophysectomy reduced porphyrins which were further reduced by daily administration of T3 or T4. These modifications in the normal females were identical in castrated males. Mitotic activity in the Harderian glands of females was stimulated by KClO4 and by hypophysectomy with or without exogenous T3. In males, castration increased mitotic activity which was suppressed by T3 and exacerbated by KClO4. Increased mitotic activity seemingly follows loss of tissue mass. The data show that thyroid hormones act directly on the Harderian glands rather than indirectly through modification of TSH synthesis/release. Female "type" glands in males are a consequence of loss of gonadal androgens by castration, or by suppression or loss of thyroid hormones by hypophysectomy or by treatment with KClO4. However, male "type" glands in females are the result of androgen treatment, and/or increased levels of thyroid hormones via reduced ambient temperatures or of photic input. We conclude that regulation of the Harderian gland appears to be different in the two sexes.