The Effect of Hypophysectomy on Gestation in the Rat

Pencharz, Richard I.; Long, J. A.

doi:10.1126/science.74.1912.206

Cited by 41 publications

(9 citation statements)

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“…The latter conclusion is consistent with other studies involving lesion of the magnocellular nuclei in the cat (Nibbelink, 1961) or of the supraopticoneurohypophysial tract in the guinea-pig (Dey, Fisher & Ranson, 1941), hypophysectomy (Pencharz & Long, 1931), prolongation of parturition by oxytocin antiserum (Higuchi et al 19866) and reversal by oxytocin of the retardation of parturition by ethanol (Fuchs, 1973), which all support an important role for oxytocin in parturition. However, increased oxytocin secretion may not be necessary for initiation of parturition, since acute or chronic oxytocin infusion can advance the onset by only a few hours (Boer & Kruisbrink, 1984), oxytocin antiserum does not delay the start (Schriefer, Lewis & Miller, 1982;Higuchi et al 19866), and oxytocin secretion is not increased until the birth of the first pup (Higuchi et al 1986 ).…”

Section: Discussionsupporting

confidence: 88%

Interruption of parturition in rats by morphine: a result of inhibition of oxytocin secretion

Russell

Gosden²,

Humphreys³

et al. 1989

Journal of Endocrinology

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Oxytocin secretion is inhibited by opioids, and oxytocin is important in parturition. The effects on parturition of morphine, a relatively selective mu-opioid receptor agonist, were studied in the rat. Morphine or vehicle with or without the opiate antagonist naloxone were administered immediately after the birth of the second pup and the subsequent course of parturition was recorded in a total of 80 rats. Both s.c. morphine (10 mg/kg) and intracerebroventricular (i.c.v.) morphine (18 micrograms through a previously implanted cannula) interrupted parturition, delaying the birth of the sixth pup after treatment to 187.3 +/- 35.9 (S.E.M.) min and 195.4 +/- 19.5 min respectively, compared with 46.4 +/- 3.7 and 66.1 +/- 17.5 min after vehicle alone. The dose of morphine given i.c.v. had no effect when given s.c. Naloxone given concurrently prevented the effects of morphine. Eventually the rate of parturition in the morphine-treated groups recovered. Perinatal pup mortality rate was not increased when morphine was given to the mothers, but it did inhibit the expression of normal intrapartum maternal behaviour. Pup mortality was increased 48 h post partum by morphine given during parturition, and it reduced the proportion of rats with normal maternal behaviour 24 h post partum. Morphine did not affect spontaneous or oxytocin-stimulated contractile activity of the parturient uterus in vitro. The concentration of oxytocin in trunk blood plasma was decreased 40 min after i.c.v. morphine (24.3 +/- 3.9 vs 39.3 +/- 6.5 pmol/l in controls), as was vasopressin (7.2 +/- 1.5 vs 19.7 +/- 4.5 pmol/l in controls). Intravenous infusion of oxytocin (2-5 mU/min for 144.3 +/- 8.2 min; total infused 448.5 +/- 61.9 mU) after i.c.v. morphine re-started parturition; all pups were born to these rats (mean time to pup 6, 110.3 +/- 12.7 min) before the i.v. vehicle-infused rats given i.c.v. morphine re-started (mean time to pup 6, 406.3 +/- 125.2 min). It is concluded that morphine given during parturition acts centrally through opioid receptors to inhibit oxytocin secretion, and impairs the expression of maternal behaviour. Reversal of the effects of morphine on parturition by i.v. oxytocin demonstrates the important role of oxytocin in fetus ejection and expulsion.

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Section: Discussionsupporting

confidence: 88%

Interruption of parturition in rats by morphine: a result of inhibition of oxytocin secretion

Russell

Gosden²,

Humphreys³

et al. 1989

Journal of Endocrinology

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“…1 and 2), coincides with the day when the pituitary can first be removed without inducing abortion (7). Presumably, rat placental lactogen (rPL) is being secreted in sufficient amounts at this time to maintain progesterone secretion by the corpora lutea.…”

Section: Effect Of Rat Placental Lactogen (Rpl) On the Biphasic Surgementioning

confidence: 99%

Termination at Midpregnancy of the Two Daily Surges of Plasma Prolactin Initiated by Mating in the Rat

1976

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The pattern of plasma prolactin following uterine cervical stimulation consists of two surges each day, one nocturnal, occurring between 0100-0900 h (lights on 0600-1800 h), and one diurnal, occurring between 1500-2100 h. This pattern of prolactin continued throughout pseudopregnancy; the last surge was observed on the morning of day 11 (day 1 was taken as the first day of diestrus of pregnancy or pseudopregnancy). Prolactin levels remained low thereafter until the spontaneous proestrous surge on the afternoon of day 12, signalling the onset of a new estrous cycle. In contrast, the two daily prolactin surges did not continue throughout pregnancy, and in fact, were terminated sooner in pregnant animals than in pseudopregnant animals. The last diurnal surge was observed on day 8 while the last nocturnal surge was observed on day 10. The early termination of prolactin surges during pregnancy correlated with the increased secretion of rat placental lactogen. However, placental extracts obtained from day 11 of pregnancy and injected in large doses failed to inhibit prolactin surges in pseudopregnant animals. Prolactin surges also continued for a longer period of time in pseudopregnant rats bearing decidualized uteri than in pregnant animals. Thus, the two major components of pregnancy that differed from pseudopregnancy, that is, the presence of rat placental lactogen or decidual tissue, did not appear to account for the early termination of prolactin surges during pregnancy.

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“…Pregnancy can be maintained and mammary development can proceed in these species after hypophysectomy provided that placental mammotropin is present together with steroid hormones (Pencharz and Long, 1931;Newton and Beck, 1939;Averill et al, 1950). Recently, Yanai and Nagasawa (1971b) Total placental weight(g) Fig.…”

mentioning

confidence: 99%

Quantitative Participation of Placental Mammotropic Hormones in Mammary Development During Pregnancy of Mice

Nagasawa

Yanai

1971

Endocrinol Japon

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SynopsisIn order to elucidate the importance of the biological role of placental mammotropic hormones in the mammary development during pregnancy, the correlations between the number and weight of placentae and some indices of mammary development were examined using nulliparous C3H/He pregnant mice. On day 8 of pregnancy, the number of placentae was adjusted to 1-12 each by removing surgically the placentae with fetuses and all the mice were killed on day 19 of pregnancy. DNA and RNA contents and RNA/DNA ratio in bilateral inguinal mammary glands and lobuloalveolar rating of the right third thoracic gland were employed as the indices of mammary development. Positive and statistically highly significant correlations were obtained between both the number and weight of placentae and each index of mammary development, and the number and weight of placentae had higher correlations with RNA and RNA/DNA than with DNA. On the other hand, pituitary levels of prolactin and growth hormone had no correlations with any index of mammary development. These results provide evidence that placental mammotropic hormones contribute quantitatively to the mammary development during pregnancy in mice and suggest that the lactogenic effect of placental mammotropic hormones would be more prominent than their mammogenic effect at late pregnancy.

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The Effect of Hypophysectomy on Gestation in the Rat

Cited by 41 publications

References 0 publications

Interruption of parturition in rats by morphine: a result of inhibition of oxytocin secretion

Interruption of parturition in rats by morphine: a result of inhibition of oxytocin secretion

Termination at Midpregnancy of the Two Daily Surges of Plasma Prolactin Initiated by Mating in the Rat

Quantitative Participation of Placental Mammotropic Hormones in Mammary Development During Pregnancy of Mice

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