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R. H. GLASS

Rabbit eggs can be fertilized in the uterus but their subsequent development in this organ is limited. Bedford (1970) transferred newly ovulated eggs to the uterus of does mated 12 to 13 hr earlier and found that 94% of the recovered eggs had been fertilized when they were examined 6 to 7 hr later. Under similar conditions, Chang (1955) found the majority of eggs at the pronuclear stage, but some of these fertilized eggs recovered 6 hr after deposition in the uterus had begun to degenerate. The deleterious effects of the uterine environment may result in rapid destruction of the newly fertilized egg. Despite occlusion of the uterocervical junction, Adams (1970) was able to recover only 53% of eggs that had been transferred to

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R. H. Glass, A. I. Spindle and R. A. Pedersen

Summary. Treatment of preimplantation mouse embryos in vitro with 10−3 to 10−1 μg actinomycin D/ml for 2 hr showed that (i) postimplantation development in vitro was inhibited most when embryos were treated at the morula stage and (ii) after the morula stage actinomycin D inhibited trophoblast outgrowth less than inner cell mass development.

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R. H. GLASS, T. P. LIN and JOAN FLORENCE

The introduction of a pipette or needle into the blastocoele has been used for measurement of the potential difference across the trophoblast (Gamow & Daniel, 1970; Cross, 1971), for aspiration of fluid (Lutwak-Mann, Boursnell & Bennett, 1960; Smith, 1970), for removal of a portion of the inner cell mass (Lin, 1969), for injection of teratogens (Lin & Monie, 1973) and for injection of cells into the blastocyst cavity (Gardner, 1968; Moustafa & Brinster (1972). Despite temporary distortion following manipulation, the blastocyst exhibits a remarkable ability to regain its original form. Capacity for normal development is also retained in most cases.

Rabbit blastocysts which contracted after microsurgery seldom implanted unless they were allowed to re-expand in culture for 3½ to 9 hr before transfer (Gardner & Edwards, 1968). In contrast to conditions in the rabbit, work in our laboratory has shown that transfer of the contracted mouse blastocyst does not limit

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RAMA A. VAIDYA, R. H. GLASS, PRAMILA DANDEKAR and K. JOHNSON

Since the introduction of the concept of capacitation, numerous investigators have attempted to define the changes that spermatozoa undergo in the female reproductive tract. Studies utilizing light and electron microscopy have failed to show alterations in sperm structure following incubation in the rabbit uterus for periods up to 15 hr, a length of time sufficient to accomplish capacitation (Bedford, 1970). The loss of tetracycline fluorescence from spermatozoa in the oestrous uterus has been suggested as an indicator of capacitation (Ericsson, 1967), but it has since been shown conclusively that this theory can no longer be considered tenable (Vaidya, Bedford, Glass & Morris, 1969).

Changes in the net negative surface charge of rabbit spermatozoa during passage through the epididymis have been demonstrated by micro-electrophoresis (Bedford, 1963). This communication describes changes

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R. H. Glass, A. I. Spindle, M. Maglio and R. A. Pedersen

Summary. Dispersed cells from cultured mouse cell lines, mouse macrophages, and inert microspheres were layered onto outgrowing mouse trophoblast in culture. The cells that settled onto the trophoblast remained round, in contrast to the elongated spreading shape they assumed on the glass substratum. The cells were readily dislodged from the trophoblast surface, whereas the microspheres were strongly adherent to trophoblast within 30 min. Scanning electron microscopy showed that trophoblast engulfed the spheres, but not the cells. Despite the lack of adhesion between cells and trophoblast, cell processes connected the two. The inability of cells to adhere to the free surface of the trophoblast could explain the trophoblast's ability to induce contact inhibition in co-cultured cells.

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R. A. VAIDYA, J. M. BEDFORD, R. H. GLASS and J. McL. MORRIS

Summary.

Removal of tetracycline fluorescence has been suggested as a test for capacitation. In the present study, a comparison is made of the time required to complete capacitation in either the uterus or the Fallopian tube, and the time in which fluorescence is lost from spermatozoa in these organs.

Capacitation requires at least 10 to 11 hr in the Fallopian tube, and a similar period is required for complete capacitation in the oestrous uterus, but tetracycline fluorescence is lost from spermatozoa in these sites within 2 hr, one fifth of the period required for capacitation. Fluorescence is not removed from spermatozoa in the uterus of immature, mature ovariectomized, pseudopregnant or progesterone-treated females, or from spermatozoa in the anterior chamber of the eye, colon or bladder; though partial capacitation occurs to a varying but significant degree in all of these sites.

It is concluded that removal of tetracycline fluorescence from spermatozoa in the female tract is not a visible concomitant of their functional capacitation.

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J. P. O'GRADY, E. I. KOHORN, R. H. GLASS, B. V. CALDWELL, W. A. BROCK and L. SPEROFF

Prostaglandins have been shown to be potent stimulants of cl steroid production in vitro (Pharriss & Wyngarden, 1969; Marsh, 1971; Speroff & Ramwell, 1970), yet prostaglandin F (PGF) given in vivo effectively inhibits progesterone secretion in rats, rabbits, guinea-pigs, sheep and the rhesus monkey (see Pharriss, Tillson & Erickson, 1972, for review). A better understanding of the possible rôle of prostaglandins has been confused by these paradoxical findings. In such studies, it would be of value to have as an experimental model, an in-vitro system in which it is possible to duplicate the inhibitory effects on luteal steroidogenesis seen with the use of PGF administered in vivo. This communication describes an in-vitro method in which sections of rabbit cl are maintained