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  • Author: M. F. McDONALD x
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The continuous collection of fluid flowing from both ends of the Fallopian tube of the ewe was attempted by placing a cannula in the ovarian end of the ampulla and a further cannula passing through the wall of the corresponding uterine horn and opposed to the utero-tubal junction. Daily recordings of fluid were made in thirty ewes over a period ranging from 3 to 106 days; observations were also made for oestrous behaviour.

There was an increase in total output of tubal fluid starting on the last day of the oestrous cycle and reaching a maximum about Day 2, after which a gradual decline occurred. A greater part of the total fluid secreted flowed through the ampullar end. Flow through the utero-tubal junction into the uterus remained low for most of the cycle, but markedly increased in all cycles 3·9 ±0·1 days after the onset of oestrus.

The peak flow through the utero-tubal junction would therefore appear to coincide with the time during which ova enter the uterus in the ewe.

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The volumes of Fallopian tube secretion which pass into the peritoneal cavity (ampullar flow) and uterus (isthmic flow) were recorded at 12-hr intervals in ovariectomized ewes, and after injection of 30 μg, 90 μg or 500 μg oestradiol benzoate (ODB). Ovariectomized ewes were also treated sequentially with progesterone, oestrogen, and, in some animals, a further series of progesterone injections in an attempt to achieve the pattern of directional flow of tubal fluid found in the intact, cyclic ewe.

A decline in total daily secretion and fluid flow followed ovariectomy and was counteracted by the administration of ODB. Both ampullar and isthmic flows were markedly increased at all dose levels of ODB until the flows were comparable with, or exceeded, those which occurred during oestrus in the intact ewe. But the sequence of maximum ampullar flow and maximum isthmic flow was reversed by ODB, the difference being further accentuated by each increase in dose level. As isthmic flow was stimulated at all dose levels of ODB, an effective restriction of the tubo-uterine junction and/or isthmus was not apparent. Progesterone in combination with ODB did not effectively restrict the isthmic flow relative to the ampullar flow.

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The secretion of fluid in the Fallopian tube is greatest about oestrus and diminishes during the luteal phase of the cycle (e.g. Perkins, Goode, Wilder & Henson, 1965). Cannulation of both ends of the Fallopian tube in the ewe and volumetric collection of the secretion has shown that most of the fluid flowed through the ampullar orifice, but that there was marked increase in flow of fluid through the tubo-uterine junction about 4 days after the onset of oestrus (Bellve & McDonald, 1968). With the ovariectomized ewe injected with oestrogen, the peak flow through the tubo-uterine junction preceded that through the ampullar end (McDonald & Bellve, 1969). The mechanism which prevents a similar premature surge in isthmic flow in the intact ewe during the pre-ovulatory period, when oestrogen is in dominance (Moore, Barrett, Brown, Schindler,
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Z. Z. Xu, M. F. McDonald, S. N. McCutcheon and H. T. Blair

Summary. In castrated rams (Romney and Poll Dorset, n = 8 for each breed), inhibition by testosterone treatment (administered via Silastic capsules) of luteinizing hormone (LH) pulse frequency, basal and mean LH concentrations, mean folliclestimulating hormone (FSH) concentration, and the peak and total LH responses to exogenous gonadotrophin-releasing hormone (GnRH) were significantly (P < 0·01) greater during the nonbreeding than during the breeding season. Poll Dorset rams were less sensitive to testosterone treatment than Romney rams. In rams not receiving testosterone treatment, LH pulse frequency was significantly (P < 0·05) lower during the nonbreeding season than during the breeding season in the Romneys (15·8 ± 0·9 versus 12·0 ± 0·4 pulses in 8 h), but not in the Poll Dorsets (13·6 ± 1·2 versus 12·8 ± 0·8 pulses in 8 h). It is concluded that, in rams, season influences gonadotrophin secretion through a steroid-independent effect (directly on hypothalamic GnRH secretion) and a steroid-dependent effect (indirectly on the sensitivity of the hypothalamo–pituitary axis to the negative feedback of testosterone). The magnitude of these effects appears to be related to the seasonality of the breed.

Keywords: season; testosterone feedback; FSH; LH; breed effect; Romney; Poll Dorset; sheep