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Biomedical subjects

S Ichikawa

Publications and source records attributed to S Ichikawa.

At least 271 records · Page 15Linked to original sources
PubMed1984

[Changes of intrauterine pressure in progesterone-treated ovariectomized rats during the second half of pregnancy].

Pregnant rats were ovariectomized on day 14 of pregnancy (sperm = day 1) and daily injected with 4 mg progesterone. The intrauterine pressure and volume of the conceptus with placenta of these rats and intact normal pregnant rats were measured every morning between day 14 and 20 of pregnancy. The average volume of the conceptus in both groups increased at an almost constant rate until day 18 of pregnancy and rapidly between day 19 and 20 of pregnancy. The intrauterine pressure of ovariectomized progesterone-treated rats increased in parallel with the volume of the conceptus until day 19 of pregnancy, suggesting a deficiency in plasticity of the uterine wall. The pressure, however, decreased significantly between day 19 and 20 of pregnancy in spite of the rapid increase of the conceptus volume. In the control rats, the intrauterine pressure gradually decreased during the second half of pregnancy, whereas the conceptus volume increased. The results suggest that estrogen secreted from the ovaries during the second half of pregnancy prevents the rise of the intrauterine pressure by improving the plasticity of the uterus. Furthermore, it could be considered that the decrease of the intrauterine pressure between day 19 and 20 of pregnancy in ovariectomized progesterone-treated rats may be caused by the estrogenic action of androgens secreted from the placenta in late pregnancy.

Androgens↗
PubMed1984

Facilitation of inspiration by intracerebroventricular injection of thyrotropin-releasing hormone in rabbits.

Effects of fourth cerebroventricular injection of thyrotropin-releasing hormone (TRH) on respiration were studied in vagotomized rabbits. Phrenic neural activity was recorded and integrated. TRH (1.0 microgram) injection facilitated phrenic neural activity and increased respiratory rate. Peak phrenic nerve activity increased slightly or showed no apparent changes when tonic activity appeared. Tidal phrenic neural activity either increased or decreased, depending on relations between peak phrenic activity and tonic activity. Results suggest that TRH facilitates central respiratory activity to induce tonic activity and increase respiratory rate.

Animals↗
PubMed1984

[The effect of androgen on the maintenance of pregnancy in progesterone-treated ovariectomized rats].

Pregnant rats ovariectomized on day 14 of pregnancy (Sperm present = day 1) were daily treated with 4 mg progesterone (P) plus androgens, and the effects of the androgens on fetal survival and intrauterine pressure were examined on day 20 of pregnancy. In the rats treated with P only, the percentage of live normal fetuses was only 40.4% of the total fetuses, 39.4% were injured fetuses having hematoma on their extremities, and 20.2% were absorbing. Intrauterine pressure was about three times higher than that in the sham-operated controls. Treatment with androgen as well significantly increased the percentage of live normal fetuses and decreased intrauterine pressure, as estrogen did. A significant negative correlation was observed between the percentage of live normal fetuses and intrauterine pressure. Androstenediol (A-diol) was most effective and its daily dose of 2 microM maintained normal pregnancy. A-diol and dehydroepiandrosterone (DHA) were more effective than androstenedione (A-dione) and testosterone (T), suggesting that the effect of the former two androgens is not by conversion to estrogen, but by their direct action on the uterine wall. 5 alpha-dihydrotestosterone, a non-aromatizable androgen, also exhibited moderate estrogenic action.

Androgens↗
PubMed1984

Effect of spironolactone on fluid volumes and adrenal steroids in primary aldosteronism.

Plasma volume (PV) and extracellular fluid volume (ECF) were determined in 7 patients with essential hypertension (controls) and in 10 patients with primary aldosteronism, while on a high Na diet (342 mEq/day) and on a low Na diet (12 mEq/day). The volume studies were repeated in 6 of the primary aldosteronism patients during treatment with spironolactone for over 3 months. Plasma renin activity (PRA), plasma aldosterone concentration (PAC), cortisol concentration, and serum Na and K concentrations were measured in all patients while on a Na-restricted diet (85 mEq/day) as well as on high-Na and low-Na diets. There were no significant changes in arterial pressure during different Na diets in any groups of patients with essential hypertension, or primary aldosteronism with and without spironolactone therapy. Spironolactone treatment normalized the arterial pressure in patients with primary aldosteronism at all Na intakes. These patients had greater values for PV and ECF than did those with essential hypertension. Spironolactone treatment reduced PV during the low-Na diet, but did not alter it during the high-Na diet. Spironolactone did not produce significant changes in ECF during either the high-Na or low-Na diets. Although there were no changes in PV and ECF in patients with primary aldosteronism due to changes in Na intake, both PV and ECF were significantly less in these patients during spironolactone treatment and in patients with essential hypertension during low-Na intake than during high-Na intake. With primary aldosteronism, PRA was depressed and PAC was elevated when compared to essential hypertension, these were not altered by different Na diets in the patients with primary aldosteronism as they were in those with essential hypertension. During treatment with spironolactone the PRA was restored to normal and showed normal changes with variations in dietary Na, but PAC remained elevated during spironolactone. Plasma cortisol was the same among those with essential hypertension and patients with untreated and spironolactone-treated primary aldosteronism. Serum K was less in untreated primary aldosteronism during all Na diets than in essential hypertension, but during spironolactone it was restored to normal. These results suggest that in primary aldosteronism the reduction in arterial pressure by spironolactone treatment does not occur simply by reductions in body fluid volumes. The long-term treatment of patients with primary aldosteronism with spironolactone does not inhibit the production of aldosterone, possibly because of enhanced activity of the renin-angiotensin system and an increase in serum K.

Adrenal Cortex Hormones↗
PubMed1984

Inhibition of in-vitro fertilization of hamster oocytes by a thiol proteinase inhibitor.

Amongst the proteinase inhibitors tested, thiolstatin, a specific inhibitor for the thiol proteinases, leupeptin and antipain, both specific inhibitors of serine- and thiol-proteinases, strongly reduced fertilization of hamster oocytes in vitro. These results suggest the possible involvement of thiol proteinase(s), as well as acrosin, in the fertilization process. A possible role for thiol proteinase in sperm adhesion to the zona pellucida is proposed.

Animals↗
PubMed1984

Distribution of action potential durations in the canine left ventricle.

The distribution of action potential durations (APD) in the left ventricle were investigated and compared to the spatial orientation of the maximum T vector (MaxTv). Eight dogs with similar vectorcardiographic spatial orientations of MaxTv were used. Action potentials were recorded from 42 to 64 sites on each isolated endocardial and epicardial specimen with glass microelectrodes. Preparations included the entire left ventricular free wall. The APD50 and APD90 had similar distributions, but the APD90 distribution was less uniform in all 8 dogs. On the endocardium, APDs were longest between the roots of the papillary muscles, and progressively shorter toward the upper edge (base) where the shortest APDs were found. On the epicardium, APDs were longest in the lower lateral region, and gradually shortened, approximately concentrically, toward the anterior and posterior bases. APDs were longer in the endocardium than in the corresponding epicardium. Maximum APD endocardial-epicardial differences were found in the lower lateral region of the ventricular free wall. Results agree with reports of ventricular recovery properties in vivo, and partly account for the spatial orientation of the MaxTv. This study adds new details, and delineates the longest and shortest distributions of APDs.

Action Potentials↗
PubMed1984

Hemodynamic effects of captopril in one-kidney, one clip hypertensive rabbits.

Hemodynamic effects of captopril were examined in chronic one-kidney, one clip renal hypertensive rabbits and normotensive controls either in normal sodium or in sodium depletion. The mean arterial pressure (MAP) of hypertensive and normotensive rabbits in sodium depletion did not differ from that in normal sodium, while plasma renin activity (PRA) was elevated by sodium depletion. The cardiac output of sodium depleted groups decreased slightly. The increase in total peripheral resistance was greater in hypertensive than in normotensive groups. The MAP in all groups was decreased by acute administration of captopril irrespective of sodium intake. The decrease in MAP in the sodium-depleted hypertensive group was correlated with the control values of PRA, but no correlation was observed in other groups. Captopril significantly reduced the cardiac output of the sodium-depleted hypertensive group, but not of the other groups. These results show that: (1) the lowering effect of captopril on arterial pressure is not mediated only by blocking of the renin-angiotensin system, and (2) the decrease in cardiac output with captopril in sodium depleted hypertensive rabbits is an important factor in the reduction in the arterial pressure.

Animals↗
PubMed1984

The effect of estrogen on passive length-tension relationship in the uterus of ovariectomized progesterone-treated pregnant rats.

Passive length-tension curves of uterine strips obtained on day 20 of pregnancy from ovariectomized, progesterone-treated (OVX-P), progesterone + estrogen-treated (OVX-PE), and intact pregnant rats (control) were determined, and the effects of ovarian hormones on the length of the collagenous framework (LZ), tension at in vivo length (TV), and distensibility (D) of the strips, which were obtained from the curves, were evaluated. LZ of circular strips, but not of longitudinal strips, of OVX-P rats was smaller than the in situ length (20 mm) of the strips, whereas the value of control rats was greater than 20 mm; TV of these strips was 4.5-fold of controls. Treatment with estrogen restored both LZ and TV to the control levels. D of both longitudinal and circular strips of OVX-P rats was smaller than the controls, estrogen increased D to longitudinal direction predominantly. Examination in Ca-free Tyrode's had no influence on any of LZ, TV or D. Results suggest that estrogen with progesterone develops the collagenous framework of the connective tissue to radial direction and distensibility of the uterine wall mainly to longitudinal direction, and thereby maintains the tension of the uterine wall to accommodate the product of conception in the rat.

Animals↗
PubMed1983

Body fluid distribution in the maintenance of DOCA-salt hypertension in rats.

Body fluid volumes and their relation to mean arterial pressure and plasma renin activity (PRA) were examined in heminephrectomized rats after 4 wk of treatment with deoxy-corticosterone acetate (DOCA) and placed on one of three levels of salt intake, either high (D-HS), normal (D-NS), or low (D-LS); sham-operated rats, which received heminephrectomy and no DOCA treatment, also received high (S-HS), normal (S-NS), or low (S-LS) intakes of salt. Body fluid volumes were measured as the distribution volumes of radioiodinated serum albumin, 35SO4, and tritiated water for plasma volume (PV), extracellular fluid volume (EFV), and total body water (TBW), respectively. Approximately the same degrees of hypertension occurred in the D-HS and D-NS rats, but the D-LS rats were normotensive. PV and EFV were increased only in the D-HS rats, with no prominent changes occurring in the D-NS rats. Intracellular fluid volume (ICF) was not changed in the D-NS rats when compared with the S-NS rats. The ratios of PV/EFV and EFV/TBW in the DOCA-treated groups on high or normal salt were not different from their controls. PRA was greatly suppressed in the D-HS and D-NS rats when compared with all other groups. In another group of D-HS rats, sodium was restricted for 2 wk; in this group the mean arterial pressure fell to control levels without significant changes in PV, but interstitial fluid volume was reduced to normal levels. These results demonstrated that 1) in DOCA-salt hypertensive rats there is expansion of body fluid volumes that are proportionally distributed among the PV, EFV, and ICF; 2) increases in body fluid volumes are not necessary for DOCA to maintain hypertension; 3) a certain minimal amount of dietary sodium is necessary for the development and maintenance of hypertension; and 4) following DOCA treatment the suppression of PRA is not due solely to expansion of body fluid volumes.

Animals↗
PubMed1983

The effect of ovarian hormones on stress relaxation in the uterus of the pregnant rat.

Tissue strip taken from rat uterine ampulla on day 20 of pregnancy was elongated at a contrast rate in Tyrode's solution at 37 degrees C to the length of a specified peak stress, and the stress decline was recorded at this length. The stress decline in uterine strips of ovariectomized progesterone-treated rats was significantly slower than those in intact pregnant rats at any different peak stress and elongation rate examined. Treatment with estradiol as well restored the physical properties to the control levels. Changing the medium to Ca-free Tyrode's solution had no effect on stress relaxation. Results suggest that estrogen with progesterone improves stress relaxation in the rat uterus during late pregnancy by changing the state of the noncontractile elements in the tissue.

Animals↗
PubMed1983

Blockage of ovulation in the explanted hamster ovary by a collagenase inhibitor.

Hamster ovaries explanted at 21:00 h on the day of pro-oestrus were incubated with talopeptin, a potent microbial inhibitor of collagenases, until 10:30 h on the next morning. A talopeptin concentration of 0.16 mM completely blocked ovulation in vitro. The blocking effect decreased markedly in ovaries excised at 23:00 h or later. The results suggest that proteolysis by collagenases is indispensable for the ovulatory process in the hamster.

Animals↗
PubMed1983

Effect of various proteinase inhibitors on ovulation of explanted hamster ovaries.

Hamster ovaries explanted at 21:00-24:00 h on the day of pro-oestrus were incubated with microbial proteinase inhibitors until 10:30 h on the next morning and the ovulatory blocking effect of these inhibitors was examined. Amongst 11 proteinase inhibitors examined, talopeptin, a specific inhibitor for metallo-proteinases, and alpha-MAPI, a specific inhibitor for serine and thiol proteinases, were the strongest blockers. These 2 inhibitors exhibited a chronological discrepancy in their blocking effect on ovulation. S-SI, plasminostreptin, elastatinal, antipain and chymostatin, which are inhibitors for serine proteinases, partly but significantly inhibited ovulation. The results suggest that, in addition to a metallo-proteinase reported previously, a proteinase which is sensitive to alpha-MAPI is essential for the ovulatory process, and that serine proteinase(s) also participate in ovulation of the hamster ovary.

Animals↗