A plasma humoral factor of extrarenal origin causing release of reninlike activity in hypotensive dogs

Plasma reninlike activity significantly increased in anesthetized and unanesthetized normal dogs after intravenous injection of plasma from nephrectomized and normal dogs that have been made hypotensive by controlled hemorrhage. The injection of plasma from nephrectomized, nonhypotensive dogs or the in vitro incubation of normal plasma with calculated proportions of plasma from nephrectomized, hypotensive dogs did not produce any changes in plasma renin concentration or angiotensin production. These results suggest the presence of renin-releasing factor of extrarenal origin which is produced and circulated in the plasma of dogs subjected to periods of hypotension by means of controlled hemorrhage. A direct or indirect action of the renin-releasing factor on the kidney in association with or in conjunction with one or more of the other mechanisms that have been hypothesized to explain the control of renin release is not as yet known. An alternative hypothesis should also be considered. It is possible that the renin-releasing factor may he an activator of the conversion of prerenin to renin and of its release from the kidney into the bloodstream. The source and chemical nature of the renin-releasing factor are not as yet known.

The maintenance of pregnancy during the pre-implantation period in mice treated with phenelzine derivatives

A number of derivatives of the mono-amine oxidase inhibitor (MAOI) compound, phenelzine, have been shown to have an anti-fertility effect, when administered both before and after implantation in mice. The action of the compounds in the pre-implantation period (days 1–6) is reversed by progesterone and by prolactin; both have to be given with 0·05 μg oestradiol/mouse during days 4 and 5 to induce implantation. When the oestrogen treatment is omitted implantation is delayed by 2–3 days. This seems to be due to a transient antagonism of the action of luteinizing hormone (LH), which is necessary for the secretion of oestrogen which in turn is necessary for implantation. In addition, the MAOI compounds appear to inhibit the release of pituitary hormones necessary for the maintenance of pregnancy. In the pre-implantation period the important pregnancy-maintaining hormone seems to be prolactin, and after implantation LH seems to become the main luteotrophin.

Maintenance of pregnancy after implantation in hypophysectomized or ovariectomized mice treated with phenelizine derivatives

Some derivatives of phenelzine have been shown to interrupt pregnancy in mice, when given after implantation, i.e. on days 7–10. Pregnancy can be maintained in mice treated with these compounds and in mice hypophysectomized on day 7 by administration of suspensions of whole mouse pituitaries, of human chorionic gonadotrophin or of progesterone given with a basic concentration of oestrogen. Prolactin was ineffective in maintaining pregnancy. The action of the phenelzine derivatives could also be reversed by 0·5–1 μg. luteinizing hormone and by 0·05 μg. oestradiol. The compounds antagonized the action of progesterone in maintaining pregnancy in ovariectomized mice and this indicates that they act on the uterus. There may be, in addition, a more central action, e.g. on the ovary or on the pituitary but this would be masked by the peripheral (i.e. uterine) effect.