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O. P. SHARMA

The neurohypophysial hormone, oxytocin, is released in response to both external and internal neural stimuli. There is considerable published evidence indicating that release of oxytocin is elicited by the suckling or milking stimulus in the cow (Folley & Knaggs, 1965; Hays & Pritchard, 1967), the goat (Hawker & Roberts, 1957), and the sheep (Fitzpatrick, 1961). There is no published report on the release of oxytocin during suckling in mares, however, and this communication presents the results of the effect of a suckling stimulus on the release of oxytocin in a lactating mare.

The effect of a suckling stimulus was examined in eight mares, all of which were studied less than 1 month after parturition. Foals were isolated from their dams for a period of 5 to 10 hr. A blood sample collected 15 min before initiation of nursing served as a control. Further blood samples were collected at 30 sec,

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O. P. Sharma

The microscopic examination of semen provides clinically important information. However, this information has been limited by the low resolution of the light microscope. Scanning electron microscopy (SEM) permits observation of free cells and has been used to study the spermatozoa of rabbit (Dott, 1969; Hafez & Kanagawa, 1973), bull and ram (Dott, 1969), monkey (Hafez & Kanagawa, 1973), man (Fujita, Miyoshi & Tokunaga, 1970; Hafez & Kanagawa, 1973; Martin & Gould, 1975), and other mammalian species (Zaneveld, Gould, Humphreys & Williams, 1971). In the present study equine spermatozoa were examined by scanning electron microscopy.

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O. P. SHARMA

Summary.

The concentrations of PGF-2α in the peripheral blood of five foaling mares were measured by radioimmunoassay. Low levels of PGF-2α were detected as early as 1 week before foaling in two of the mares. These levels increased steadily, reaching a peak (1·74 ±0·44 ng/ml) during fetal expulsion. A relatively high PGF-2α level was found in samples collected 60 min after foaling.

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O. P. SHARMA and R. L. HAYS

Department of Dairy Science, University of Illinois, Urbana, Illinois 60801, U.S.A.

(Received 28th April 1975)

The consecutive insemination of an oestrous female by two different males has often been reported to yield disproportionate numbers of offspring. This disparity in the number of offspring has been suggested as being independent of the number of spermatozoa from each sire (Allen & Champion, 1955; Edwards, 1965; Roche et al., 1968; O'Reilly et al., 1972). The heterospermic impregnation technique has also been used to determine the effect of semen storage and semen diluents and to evaluate the relative fertility of males (Roche et al., 1968; Beatty et al., 1969). In the mouse (Lewis & Wright, 1935) and rat (Blandau & Money, 1944) sperm transport is almost instantaneous and it might be expected that the spermatozoa deposited by the first sire would be at an advantage in reaching the site of fertilization before the spermatozoa

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O. P. SHARMA and R. L. HAYS

Summary.

The oxytocic activity of the jugular blood plasma of bulls before and after copulation, ejaculation into an artificial vagina, massage of the seminal vesicles and ampullae and stimulation with an electroejaculator increased from below 0·01 μU/ml to a peak level varying from 2 to 1000 μU/ml 4 to 6 min after ejaculation or 6 to 9 min after the start of electrical or manual stimulation.

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O. P. SHARMA and R. L. HAYS

Summary.

Electrical stimulation of 10 to 15 V for 1 to 2 sec applied to the dorso-lumbar region of ageing male rats significantly increased the number of times oestrous females were mounted.

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E. B. KREHBIEL, J. R. LODGE and O. P. SHARMA

Sperm transport through the female reproductive tract in mammals has been studied by several investigators. The results from these studies have shown that in the mouse (Lewis & Wright, 1935), the rat (Blandau & Money, 1944), the hamster (Yamanaka & Soderwall, 1960), the cow (VanDemark & Hays, 1951; Hays & VanDemark, 1952), and the ewe (Mattner & Braden, 1963), spermatozoa are present in the oviducts within minutes of mating or insemination. A rapid transport of spermatozoa to the rabbit oviduct has not previously been reported. The interval between mating and the finding of spermatozoa in the oviducts has ranged from 1 hr (Chang, 1952) to 3 to 4 hr (Braden, 1953) and, for sufficient spermatozoa to fertilize all of the eggs, to as much as 5 to 6 hr (Adams, 1956;

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S. M. L. C. Mendis-Handagama and O. P. Sharma

The effects of neonatal treatment with the reversible goitrogen, 6-n-propyl-2-thiouracil (PTU) on the volumes of testicular interstitial components, the number and average volume of Leydig cells, and the steroid secretory capacity of testis and Leydig cells of rats at 135 days of age were investigated. Rat pups were hypothyroid from birth to 25 days of age following the addition of 0.1% (w/v) PTU to the drinking water of the mother. Treatment was stopped at 25 days and the pups subsequently returned to a euthyroid state. Control rat pups were raised without adding PTU to drinking water of the mother. On day 135, one testis from each rat (n = 5 per group) was fixed by whole body perfusion for microscopy and stereology, and the ipsilateral testis was used for steroid secretion analysis using an in vitro testis perfusion system. Average testis volume was 84% greater in PTU-treated rats than in controls. This increase resulted from increases in both the seminiferous tubule (86%) and the interstitial (80%) volumes. Moreover, absolute volumes of all testis components in PTU-treated rats were significantly (P < 0.05) greater than those of controls; the highest volume increase was observed in the lymphatic space (147%). The number of Leydig cells per testis was nearly doubled, but the average volume of a Leydig cell was decreased by 25% in PTU-treated rats compared with controls. Steroid secretion per testis was not significantly different between control and PTU-treated rats; however, steroid secretion per Leydig cell was significantly lower in PTU-treated rats than in controls. These results demonstrate that the neonatal administration of PTU causes Leydig cell hyperplasia. However, the normal androgenic status of these animals is maintained by hypotrophy associated with reduced steroid secretion of individual Leydig cells at maturity.