Age Changes tn the Ovary 14.'3 



closely related embryologically, the ovary may undergo 

 considerable hyperplasia in utero, which is followed later by 

 degeneration and regression. 



^lore numerous papers emphasize the converse finding 

 that the young postnatal ovary of various experimental 

 animals is insensitive to hormones. Absolute insensitivity of 

 the ovaries of four-week-old rabbits has been reported by 

 Hertz and Hisaw (1934), and Parkes (1943) has shown that 

 female rabbits do not respond to a gonadotrophin preparation 

 from horse pituitary glands until they weigh more than 1 • 3 

 kg. Adams (1953) reports that ten-week-old rabbits are 

 insensitive to a similar type of pituitary extract whatever 

 their weight. Their capacity to respond increases rapidly 

 during the next two weeks and super-ovulation can be 

 achieved when a rabbit is three months old. The ova which 

 are released can be fertilised but fail to develop in the imma- 

 ture animals, not, however, because the ova themselves are 

 inadequate but because the necessary uterine conditions have 

 not yet been achieved. The ova will develop fully if they are 

 transferred to the uterus of a mature host. 



The duration of this early phase of absolute insensitivity of 

 the ovaries varies considerably from one species to another. 

 It appears to be very short in the rat (Price and Ortiz, 1944) 

 and the young heifer. Harden (1951) has reported that a 

 three- week-old calf will respond to injections of gonadotro- 

 phin at least as w^ell as an eight to eleven-month-old calf. On 

 the other hand, young female monkeys are insensitive for 

 relatively much longer. In general, the interstitial tissue of 

 the ovary responds at an earlier age than does the follicular 

 apparatus, which seems to grow slowly but autonomously 

 until the stage of antrum formation is reached. 



{b) Changes at puberty 



In some species the pituitary gland contains gonadotrophin 

 even before the animal is born. The hormone gradually 

 accumulates in the gland as the age of puberty is approached 

 (Lauson, (iolden and Severinghaus, 1939) but none is released. 



