The temporal and direct relationships between serum estradiol (E) and progesterone (P) levels and uterine blood flow (UBF) and intrauterine oxygen tension (IU PO2) were examined in guinea pigs between days 1 and 8 of pregnancy. Both UBF and IU PO2 were measured in situ using a noninvasive electromagnetic blood flow monitor and needle oxygen electrode, respectively. Serum P levels remained relatively constant throughout the first 8 days of pregnancy. In contrast, serum E levels declined to basal levels between days 1 and 3, and then subsequently rose between days 4 and 7 before again falling to basal levels by day 8. The changes in UBF and IU PO2 paralleled those of serum E levels, both exhibiting a rise between days 5 and 6. The direct effect of oil, E, or P injections on UBF and IU PO2 measurements in ovariectomized animals indicated that E induced a dramatic rise in both uterine parameters, whereas both measurements remained at basal levels after oil or P treatment. The results of this study indicate that UBF and IU PO2 levels are directly regulated by the cyclic fluctuations in serum E. The temporal relationship between the days 4 to 7 rise in serum E, UBF, and IU PO2 levels and the timing of blastocyst implantation suggest that these events are involved in uterine preparation for nidation in the guinea pig.

To investigate the cellular and subcellular distribution of glucose transporters in skeletal muscle, the glucose transporter isoform GLUT4 was localized in human muscle by electron microscopy via immunogold labeling with monoclonal (1F8) or COOH-terminal peptide polyclonal (ECU4) antibody and in isolated rat membranes by Western blot. There was no labeling of GLUT4 in endothelial cells of the capillaries. There also was no labeling of GLUT4 on the surface plasma membrane (sarcolemma) under either basal or insulinstimulated conditions. Specific labeling for GLUT4 was clearly observed in two compartments: within the triad (on terminal cisternae and transverse tubules) and on an intracellular compartment, possibly sarcoplasmic tubules. Isolated triad membranes from rat muscle also contained substantial quantities of GLUT4 transporter, but there was no detectable GLUT4 protein in isolated sarcolemmal membranes. These data suggest a possible mechanism that involves glucose transport across the muscle cell at the transverse tubule membrane, not the sarcolemma. Diabetes 40:150-54, 1991 V ilaro et al. (1) reported that the insulin-regulatable glucose transporter (GLUT4) is found predominantly in capillary endothelial cells of muscle and adipose tissue. This intriguing observation suggests that control of glucose transport by insulin may be primarily at the level of the capillary rather than the cell membrane as previously believed. Because of the importance of this question, we have further investigated the cellular and subcellular distribution of GLUT4 in human skeletal muscle via immunocytochemical localization. In addition, we have isolated triad and sarcolemmal membranes from rat skeletal muscle to determine the localization of the GLUT4 transporter. Our data clearly demonstrate that there is no GLUT4 in capillary endothelium in human muscle. Moreover, no GLUT4 transporters are detectable in the surface plasma membrane (sarcolemma) under either basal or insulin-stimulated conditions. Instead, the transporters are concentrated in the triad (transverse tubules and terminal cisternae) and in an intracellular compartment, possibly sarcoplasmic tubules. In agreement with this distribution pattern in situ, we found high concentrations of GLUT4 protein in isolated triad membranes from rat muscle but no detectable amounts in isolated sarcolemma. RESEARCH DESIGN AND METHODSFor this study, nondiabetic lean human volunteers underwent a muscle punch biopsy of the vastus lateralis muscle in the basal state after an overnight fast and during the final 30 min of a 2-h hyperinsulinemic-euglycemic clamp at 40 mil • nrr 2 • min" 1 . Informed consent was obtained before the biopsy after the nature and risks of the procedure had been fully explained. Muscle biopsies and membrane fractions were fixed in 4% paraformaldehyde/1 % glutaraldehyde at 4°C for 2 h, followed by 1% osmium tetroxide at 4°C for 1 h and embedding in LR white resin. Fixatives were made in 0.1 M phosphate buffer at pH 7.4. LR white resin (medium grade; Ted Pella, Redd...

The effects of alloxan-induced diabetes mellitus on rat ovarian structure and function were examined throughout pseudopregnancy (PSP). Animals received either saline (C) or alloxan (40 mg/kg) treatment on the day of proestrus (PA) preceding PSP or on day 1 (D-1A) of PSP (day 0 = ovulation). Serum samples were analyzed by radioimmunoassay for progesterone (P) and 17-beta-estradiol (E) levels and compared with the corresponding changes in ovarian and uterine weights in C, PA, and D-1A rats. In addition, the effects of daily treatment with 6 IU ovine insulin (AI) on serum P levels were assessed in D-1A-treated rats and compared with controls. Alloxan treatment effectively elevated blood glucose levels (P less than or equal to 0.01) in PA and D-1A groups as compared with controls or AI rats. Alloxan treatment reduced both ovarian and uterine weights of PA and D-1A groups as compared with C and AI rats. Serum P levels were significantly reduced in PA (P less than or equal to 0.01) and D-1A (P less than or equal to 0.05-0.01) rats as compared with control rats throughout PSP. Daily insulin treatment reversed the suppressive effects of D-1A treatment on serum P levels, but did not restore luteal function to control levels. Neither C nor D-1A groups exhibited any marked differences in serum E levels throughout PSP. The results of these studies indicate that the administration of alloxan before the onset of PSP effectively inhibits luteal function, whereas D-1A treatment induces early luteolysis as compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)

The alterations which occur in the total uterine blood flow (UBF) during early pregnancy in the guinea pig were determined using electromagnetic blood flow probes. Between days 4 and 6 postcoitum, UBF rose from basal levels of 1.2 ml/min to peak levels of 3.0 ml/min. The elevated levels corresponded temporally with the onset of blastocyst implantation. Between days 7 and 8, UBF declined to basal levels. In guinea pigs possessing three pregnancy sites per uterine horn on days 10–20, obvious regional differences in UBF were observed. Consistently higher UBF measurements were monitored from uterine segmental arteries supplying the tubal and cervical thirds of the uterus than from those distributed to the middle third of the uterus. These data indicate that regional variations in UBF exist in the guinea pig which may be involved in the regulation of pregnancy site selection or subsequent placental-fetal growth.

The relationships between experimentally induced deciduoma formation, circulating estradiol (E) and progesterone (P) levels and alterations in uterine blood flow (UBF) were studied between days 4 and 15 of pseudopregnancy (PSP: day 0 = ovulation) in rats. Blood flow was measured with an electromagnetic blood flow monitor and serum analyzed for E and P levels by radioimmunoassay. Neither uterine trauma on day 4 of PSP nor the site of trauma had any direct influence on altering UBF. A dramatic increase in UBF occurred in response to stromal proliferation on days 5–6 and continued to remain above sham-operated control levels through day 9. These vascular changes correlated temporally with the day 9 peak in uterine weight resulting from deciduoma formation. Both uterine weight and vascular fluctuations in deciduoma-bearing rats were related to the cyclic changes in E/P ratios between days 5 and 8 of PSP. A decline in UBF preceded deciduoma regression between days 9 and 15 of PSP. These results suggest that an increase in UBF is causally associated with the formation and maintenance of deciduoma in the PSP rat and that deciduoma regression may result from a subsequent decline in UBF rates. Both factors may be directly dependent on fluctuating E/P ratios.