Ernest L. Lahr

Maternal Behavior Induced in Virgin Rats by Prolactin

Summary In virgin rats aged 67-81 days, with ovaries stimulated by Prolan or F.S.H. administration during 5 days, the injection of purified and previously heated prolactin induced maternal behavior in 6 of 10 rats after 6-10 injections. Previous conditioning by concaveation was limited to a single 12-hour period in 4 of these rats. The maternal instinct, in somewhat varying degrees, was exhibited by all these rats while the daily subcutaneous injections were in progress. Six of 7 rats of the control and F.S.H. injected groups, all showing little or no maternal behavior during a 25-day test, later developed or greatly accentuated their maternal behavior after 1 to 8 days treatment with prolactin. Four rats which showed no maternal behavior under prolactin also later failed to show such behavior after repriming and 13 days of administration of unfractionated pituitary extract. Prolactin is the anterior pituitary hormone specifically concerned in the activation of maternal behavior in virgin rats.

Temporary Suppression of Estrous Cycles in the Rat by Prolactin

Conclusions In the regulation of the ovarian activity of rats prolactin is shown to be capable of playing a part, directly or indirectly. Prolactin can not be summarily omitted from lists of pituitary principles having action on the gonads of mammals. The suggestion of Dresel that lactation anestrus in mice is induced by prolactin is supported by these tests on mature non-parous rats. But under effective prolactin dosage the corpora of rats remain large, and at the age of 10-12 days their large cells show no clear evidence of degeneration. The failure of daily injections of low or moderate doses of progesterone to affect the estrous cycles of rats suggests that in this rodent, though the corpus luteum hormone plays its part, it is perhaps not the hormone primarily responsible for the anestrous of either gestation or lactation.

On the Protein Nature of Prolactin and of Follicle-Stimulating Hormones:

Summary Prolactin is a protein-like substance which at pH 8.0 is almost completely destroyed by trypsin in 2 hours at 37°C. In confirmation of previous work though using the bird testis instead of the rodent ovary to test potency, it is found that the follicle-stimulating hormone obtained from the anterior pituitaries of cattle is very rapidly destroyed by trypsin under the above-named conditions. The methods used in the separation and purification of prolactin suggest that this hormone is a protein, but since it has not yet been obtained in a pure state the possibility of its adsorption on inert protein is not thus excluded. It is therefore desirable to learn whether prolactin is affected by tryptic digestion. That prolactin is rapidly destroyed by trypsin is shown by the data of Table I. Almost complete destruction in 2 hours by a purified trypsin is obtained. The prolactin preparation used in this test was relatively pure and highly potent. Both the control and digest were, at the beginning of the test, at pH 8.0 and were similarly kept at 37°C. At pH 8.0 we have repeatedly found that prolactin will withstand boiling for 1 hour with only slight or moderate loss of potency. No earlier observations on the effect of digestive enzymes on prolactin have been reported. The rapid destruction of follicle-stimulating hormone (F.S.H.), obtained from the anterior pituitaries of beef by methods previously described, 1 is shown by the data of Table II. The testes of both birds given F.S.H., heated at pH 8.0 but not subjected to trypsin, are indicated as having increased by something more than 500%. The testes of all of the 4 birds receiving the trypsin digest (birds I and J got double dosage) showed only or relatively insignificant gains in weight. Since size increase in testes of the immature dove represents a specific response to the F.S.H. (here the weight is not increased by a Prolan B factor) this result has definite significance. Under these conditions still other relatively pure preparations of F.S.H. have been shown to withstand heating to 37° for 2 and for 4 hours with little loss of potency. A quite different test for F.S.H. potency has been used in another study; that test likewise shows that trypsin rapidly destroys the F.S.H. derived from both pituitary and pregnant urine.

Response of Adult Rat Testes Sex Accessories and Adrenals to Injections of Prolactin.

Summary In adult (not senile) rats injected during 8 to 22 days with 10 or 20 units per day of prolactin the weights of testes were not diminished. By this dosage the weight of Cowpers glands are apparently decreased, and that of the adrenals increased. In relatively high dosage during similar periods follicle-stimulating hormone (+ some thyreotropic) and Prolan are found, confirming earlier work of others, to have almost negligible power to cause an increase of size in such testes. Prolan led to marked enlargement of the seminal vesicles and prostate, and in the heavy dosage used it was apparently adverse to body growth.