GROWTH-PROMOTING ACTIVITY OF PREGNANT RAT PLASMA AFTER HYPOPHYSECTOMY AND AFTER THYROIDECTOMY1

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Abstract
Growth promoting potency of rat blood plasma, as evaluated by the tibial assay, decreased after thyroidectomy, and increased during normal pregnancy. Thyroidectomy did not interferewith the increased level during pregnancy. Hypophysectomy of the pregnant rat did not reduce thegrowth promoting activity of plasma to the extent which it did in non-pregnant rats. Thyrotrophic activity (assayed by I131 uptake and thyroid morphology of hypophysectomized recipients) was demonstrable in plasma from both pregnant and non-pregnant thyroidectomized rats. Similar volumes of plasma from intact pregnant or non-pregnant rats elicited no response in the thyroids of recipients. Adrenocorticotrophic activity was not detected at the doses injected (by weight and morphology of the adrenals of recipients) in plasma from any type of donor (normal, thyroidectomized, hypophysectomized rats, pregnant or non-pregnant). Gonadotrophic activity was not detected in plasma of any type of donor, as judged by ovarian morphology of recipient hypophysectomized rats. However, judged by the follicular development in the donors, follicle-stimulating substances arc present in plasma late in pregnancy both in normalpregnant and thyroidectomized-pregnant donors, but not in hypophysectomized-pregnant donors. Luteotrophic substances were present both in hypophysectomized-pregnant and thyroidectomized-pregnant rats, as judged by maintenance of the corpora lutea in these donors.