Abstract. Congenital hypothyroid mutant male rdw rats have enlarged testes in adulthood with dwarfism accompanied by infertility. To explain how rdw rats acquire enlarged testes in adulthood, we compared age-matched normal (N) rats at various developmental stages for blood levels of hormones, thyroxine (T4), follicle stimulating hormone (FSH), luteinizing hormone (LH) and testosterone (T), and investigated whether T4 therapy (rdw+T4) from 3 weeks of age (w) until adulthood could induce recovery of fertility in rdw rats, as well as how rdw+T4 affected hormonal patterns. Testes weights of rdw rats were higher than those of N rats at 19 w in adulthood though it was low during development. Serum T4 values in rdw rats were markedly lower than those in N rats but steadily increased up to 19 w. The serum FSH values in rdw rats were lower than those in N rats at all ages, and neither serum LH nor T value was significantly different at any age. The testes weight of rdw+T4 rats was significantly higher than that of N rats at 13 w with recovered growth, and was higher than that of rdw rats at 19 w. When they were mated with proestrous females after 16 w, all females became pregnant and gave birth to a normal number of pups. The T4 and FSH values of rdw+T4 rats were significantly higher than those in rdw rats, but similar to those in N rats in adulthood. The results suggest that even low levels of circulating thyroid hormone (TH) in rdw rats stimulate the development of their testes, probably through Sertoli cells, resulting in the enlarged adult testes without fertility, and that a sufficient circulating TH level from the immature stage plays a pivotal role in restoring mating activity, probably through FSH-mediated action towards adulthood.

Partial ovaries from mice, hamsters, rabbits, Japanese monkeys and rats have survived deep-freezing and returned to a normal morphological state after being thawed and transplanted into the rat uterine cavity. This report describes the ice-free cryopreservation of mouse and other ovaries at -196 degrees C by vitrification. The vitrification solution was based on the solutions reported by Rall & Fahy [16]. After ovaries had been exposed to the vitrification solution, they were frozen, with their suspending medium, by liquid nitrogen. After freezing, the ovaries were thawed in 37 degrees C water. The viability of the previously frozen ovarian tissue was tested by transplanting it into the uterine cavity of pseudopregnant rats. Seven days after transplantation, the ovaries were removed with the rat uterus, and stained with haematoxylin and eosin for histological examination. Survival of the frozen-thawed the ovaries in the rat uterine cavity demonstrates that these ovaries can tolerate exposure to osmotic dehydration and vitrification in a concentrated solution of cryoprotectant and are then immunologically acceptable to the uterine cavity.

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The age-related changes in the number of follicles classified according to size were investigated. The number of large follicles expected to ovulate spontaneously was not influenced by age, though the number of small follicles 250-549ƒÊm in diameter, re