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  • Author: G. H. ZEILMAKER x
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Prolongation of lactation beyond its natural duration has been induced in rats (Bruce, 1958, 1961; Nicoll & Meites, 1959) and mice (Parkes, 1926; Selye & McKeown, 1934; Fekete, 1940; Mühlbock & Tengbergen, 1961; Zeilmaker, 1968) by regular replacement of the suckling litter. Measurement of milk yield of mice bearing pituitary grafts and subjected to prolonged lactation, suggested that milk production occurs in a cyclic fashion (Zeilmaker, 1968). In the present study, this phenomenon has been re-investigated using mice with or without pituitary grafts under the kidney capsule. Moreover, the effect of ovariectomy on lactation was explored and attempts were made to correlate the fluctuations in milk yield with the occurrence of oestrous cycles. Experiments were performed with (C3H×020)F1 mice, caged singly. During the 2nd week of pregnancy three of the four experimental groups of animals received two syngenetic
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It has repeatedly been observed that transfer of zygotes, two-cell stages or blastocysts to the oviduct of a recently mated mouse leads to implantation and subsequent pregnancy (Bittner & Little, 1937; Tarkowski, 1959; Zeilmaker, 1968).

Studies in vitro have shown that the development of the mouse zygote to the blastocyst stage is frequently hampered by a failure to pass the two-cell stage (Whittingham, 1966). For this critical phase in the development, the ampullar region of the mouse oviduct must be present, either in vivo (Whittingham, 1968a; Cross & Brinster, 1970) or in vitro (Biggers, Gwatkin & Brinster, 1962; Whittingham, 1968b, c).

The question arises whether the critical contribution of the oviduct is dependent on the hormonal conditions prevailing after oestrus, since Whittingham (1968c) demonstrated, in explantation studies with oviducts containing zygotes, that the cycle stage at which the oviducts were explanted influenced egg development.

The present study is concerned with

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The effect of a single subcutaneous injection of ergocornine methanesulphonate on early pregnancy in mice was studied. In all animals receiving 0·5 mg (4 ♀♀ or 0·25 mg (8 ♀♀ of the drug on Day 4, pregnancy was terminated, but only two of four pregnancies were terminated with 0·1 mg and none with 0·05 mg.

Thirty-two mice in groups of four were given 0·25 mg ergocornine from Day 0 through Day 7 of pregnancy. All mice that received the drug on Days 3 or 4 terminated their pregnancy. On all other days, the animals delivered normal litters. It is quite probable that the action of ergocornine in mice is similar to its action in rats.