Cytological effects of TSH on the thyroid of hypophysectomized rats with and without previous administration of actinomycin D. An electron microscope study.

The present paper is concerned mainly with two problems: the fine structural changes of the thyroid gland after hypophysectomy and the inhibition of the endocytic effect of TSH by actinomycin D. It has been well known that the thyroid gland is stimulated by the TSH secreted from the adenohypophysis. Numerous papers have been published dealing with the electron microscopy of the thyroid gland following the injection of TSH (WISSIG 1963, FUJITA 1963, 1968, SHELDON et al. 1964, STEIN and GROSS 1964, WETZEL et al. 1965, SELJELID 1967 a, b, c, etc.). However, as to the fine structure of the thyroid after hypophysectomy, information is scarce except for the papers of DEMPSEY and PETERSON (1955), KUROSUMI (1964, personal communication), WETZEL et al. (1965), SELJELID (1967), and SCHWARZ (1967); finer pictures and more detailed descriptions seem needed. Numerous authors have reported that large droplets appear in the apical part of the follicular cell from 5 minutes to several hours after injection of TSH. These large droplets have recently been regarded as an endocytic reabsorbed colloid by autoradiographic and microinjection methods (SHELDON et al. 1964, STEIN and GROSS 1964, BAUER and MEYER 1964, EKHOLM and SMEDS 1966, SELJELID 1967 a, b, FUJITA 1968). The present authors who have studied the effect of TSH and actinomycin D on the thyroid gland of the hypophysectomized rat, noticed by chance that the endocytic action of TSH is inhibited by actinomycin D.