The vaginal smears of rats as influenced by frequent examinations

Abstract

T W O FIQURESThe recent observation of Wade and Doisy ('35) that vaginal smears characteristic of estrus could be obtained in castrated rats without the presence of the estrous hormone has led us to wonder if the sharp division of the estrous cycles into stages as described by Long and Evans ('22) is still warranted. Their classical paper and that of Stockard and Papanicolaou ('17) have been far reaching in the problem of sex physiology. These publications and many others dealing with the estrous cycles in mammals were based upon the cellular structure of the vaginal smear.Quite in contrast is the recent report of Wade and Doisy establishing beyond doubt that the frequency of the smear determined the histological picture in castrated rats. Three examinations a day with a cotton swab caused positive smears in 25 per cent of their rats. I n our colony we had never observed any smears whose positive nature we considered due t o the method of examination, but our observations (unpublished) were limited to two smears daily. The smears were made by lavaging the vaginal canal with a little saline by means of a medicine dropper. Accordingly, it occurred to us that quite different results might be obtained if the rats were examined four times a day. This we have done in castrated and normal rats using the pipette or lavage method of examination, as well as the cotton swab method. A comparison of these data are presented in this paper.

The activation of sexual behaviour in cats by the subcutaneous administration of oestrogen

“…The relation between vaginal and behavioural oestrus in ovariectomized cats treated with oestrogens differs from that seen in normal cats showing oestrous cycles. Under natural conditions the appearance of a cornified smear is synchronized with oestrous behaviour (Michael, 1961 (Everett, 1940) and guinea-pig (Young et al 1941 Hu & Frazier (1935), Emery & Schwarbe (1935, 1938, have drawn attention to the fact that even gentle trauma will induce stratification in the vaginae of spayed rats in the absence of administered oestrogen. A similar phenomenon was seen in the spayed cat, where fluctuations (20-30%) in the cornification index were observed in control animals, smeared on alternate days for 60 days, to which ethyl oleate only was administered daily.…”

“…These results are in line with those obtained in other species mentioned above, in which it was found that vaginal cornification can be produced by doses of oestrogen too small to SUBCUTANEOUS OESTROGEN AND SEXUAL BEHAVIOUR 271 confirm that the vaginal threshold is below that of the behavioural responses under conditions of prolonged administration of low doses of oestrogen. Wade & Doisy (1935), Hu & Frazier (1935), Emery & Schwarbe (1935, 1938, have drawn attention to the fact that even gentle trauma will induce stratification in the vaginae of spayed rats in the absence of administered oestrogen. A similar phenomenon was seen in the spayed cat, where fluctuations (20-30%) in the cornification index were observed in control animals, smeared on alternate days for 60 days, to which ethyl oleate only was administered daily.…”

Stimulational seizures without pseudopregnancy in white rats.

“…The technique of taking vaginal smears to determine estrous cycles was similar to that of Emery and Schwabe (1), except that a solution of methylene blue dye in distilled water was used instead of saline solution. The technique, which proved satisfactory in preliminary trials, was briefly as follows: A medicine dropper had been modified by elongating the point and fire-polishing its edges.…”

Isometric Contractions of Isolated Rat Uterine Muscle: Relation to Estrous Cycle and Pregnancy

“…Where there was doubt about the staging of a cycle, or if an intermediate stage was encountered, that muscle was not used. Care was taken not to induce a pseudo-pregnancy by rough handling when obtaining the vaginal smear and the rats were never examined more than once a day (9).…”