Biomedical subjects

Low-Tone Ho

Publications and source records attributed to Low-Tone Ho.

58 records · Page 4Linked to original sources

PubMed2002

Stimulatory effects of hyperprolactinemia on aldosterone secretion in ovariectomized rats.

BACKGROUND: To evaluate the effects of hyperprolactinemia on aldosterone secretion and its mechanisms of action in ovariectomized (OVX) rats. METHODS: Hyperprolactinemia was induced by the transplantation of rat anterior pituitary (AP) glands under the kidney capsule for 6 weeks in female rats. Control rats underwent cerebral cortex (CX) transplantation. Four weeks after transplantation, the rats were OVX 2 weeks before decapitation. After decapitation, the trunk blood was collected, and the adrenal glands of CX- and AP-grafted rats were prepared as zona glomerulosa (ZG) cells for in vitro study. RESULTS: Plasma prolactin and aldosterone in the rats were increased by AP gland transplantation. In the in vitro study, the basal aldosterone secretion by the adrenal ZG cells was higher in AP-grafted rats than in CX-grafted rats. The AP-grafted group showed increased responsiveness to angiotensin II (10(-8) M), KCl (8 x 10(-3) M), or 8-bromo-adenosine 3',5'-cyclic monophosphate (8-br-cAMP; 10(-4) M, a membrane-permeable analogue of cAMP) with regard to aldosterone secretion as compared with the CX-grafted group. N-(2-[p-Bromocinnamylamine]ethyl)-5-isoquinolinesulfonamide (H89; 10(-6), 10(-5) M, a protein kinase A inhibitor) or tetrandrine (10(-5) M, a blocker for both L-type and T-type Ca2+ channels) induced a greater suppression of aldosterone secretion in the AP-grafted group than in the CX-grafted group. No significant differences between the CX- and AP-grafted groups were observed, however, with regard to the adrenocorticotropichormone (10(-9) M)-, forskolin (10(-5) M, an adenylyl cyclase activator)-, or nifedipine (10(-5) M, an L-type Ca2+ channel blocker)-induced responsiveness of aldosterone secretion. In addition, there was no difference in the expression of desmolase (i.e., cytochrome P450 side-chain cleavage enzyme) in ZG cells between AP- and CX-grafted rats. The conversions of 25-OH-cholesterol into pregnenolone in the presence of trilostane (an inhibitor of 3beta-hydroxysteroid dehydrogenase) and corticosterone into aldosterone, as well as the expression of the steroidogenic acute regulatory protein in ZG cells, were greater in AP-grafted rats than in CX-grafted rats. CONCLUSIONS: These results suggest that hyperprolactinemia increases basal, angiotensin II- and KCl-stimulated aldosterone secretion by ZG cells in OVX rats through activation of T-type Ca2+ channels, the post-cAMP and protein kinase A pathway, cytochrome P450 side-chain cleavage enzyme, and aldosterone synthase, as well as by causing increased expression of steroidogenic acute regulatory protein in ZG cells.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed2002

Effects of fasting on corticosterone production by zona fasciculata-reticularis cells in ovariectomized rats.

BACKGROUND: To investigate the function and mechanism of fasting on the production of corticosterone in vitro by zona fasciculata-reticularis (ZFR) cells from ovariectomized (OVX) rats. METHODS: Female rats were OVX for 4 days before decapitation. Rats were fed or fasted for 1 day before experiment. ZFR cells from fed and fasted rats were incubated with adrenocorticotropic hormone (ACTH), forskolin, 8-bromo-3',5'-cyclic adenosine monophosphate, SQ22536, nifedipine, chelerythrine chloride, trilostane or steroidogenic precursors at 37 degrees C for either 60 or 30 minutes. Corticosterone, pregnenolone concentrations in spent media, and the intracellular adenosine 3',5'-cyclic monophosphate (cAMP) concentration were determined by radioimmunoassay. The effects of fasting in response to ACTH on the protein expressions of steroidogenic acute regulatory protein (StAR) or cytochrome P450 side-chain cleavage enzyme (P450scc) in ZFR cells were determined by Western blot analysis. RESULTS: The concentration of plasma corticosterone in fasted rats was significantly higher than that in fed rats (P<0.01). One-day fasting significantly increased the responsiveness of ZFR cells to ACTH, forskolin, and precursor-stimulated corticosterone productions and to forskolin-stimulated cAMP accumulation. The corticosterone production was reduced in fasted group when adenylyl cyclase was inhibited by SQ22536. The fasting-enhanced level of corticosterone production in ZFR cells was decreased by the administration of nifedipine but not altered by that of chelerythrine chloride. Fasting significantly increased trilostane-stimulated production of pregnenolone in ZFR cells. The activities of enzymes which converting cholesterol, pregnenolone, progesterone, and deoxycorticosterone to corticosterone and the expressions of StAR in ZFR cells were greater in fasted rats than in fed rats. CONCLUSIONS: This study demonstrated that fasting increased the release of corticosterone and the accumulation of cAMP by rat ZFR cells. The action mediated through enhancing the responsiveness to ACTH stimulation, cAMP cascades and the activity of L-type calcium channels. The activities of steroidogenic enzymes including P450scc, 3beta-hydroxysteroid dehydrogenase, 21-hydroxylase, and 11beta-hydroxylase were all enhanced by the fasting treatment.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMedDate not supplied

Waist circumference predicts metabolic cardiovascular risk in postmenopausal Chinese women.

OBJECTIVE: The purpose of the study is to compare the differences in metabolic cardiovascular risk factors among postmenopausal Chinese women with or without abdominal obesity. DESIGN: The study is a cross-sectional, population-based, comparative cohort study. Each participant received anthropometric measurements and a 75-g oral glucose tolerance test after an overnight fast. The homeostasis model assessment for insulin resistance and the insulin sensitivity index, ISI, were used as measures of insulin resistance. A "metabolic cardiovascular risk score" was calculated from fasting insulin, glucose, lipids, and blood pressure. General linear models (GLM) were fit to examine the relation of waist circumference (WC) to insulin resistance and metabolic risk scores.(0,120). RESULTS: According to the International Obesity Task Force obesity criteria for Asians, 57 women had abdominal obesity (WC >/= 80 cm), and 58 had WCs less than 80 cm. The two groups were comparable in demographic variables and body mass index (BMI). The women with larger WCs were more insulin-resistant than their counterparts. The metabolic risk scores were significantly higher in women with abdominal obesity than in those without it. The results from the GLM showed that WC was an independent predictor of insulin resistance and metabolic risk scores after controlling for demographic variables (0.06- and 0.29-unit increases in homeostasis model assessment for insulin resistance and metabolic risk scores per 1 cm change in WC). Moreover, BMI neither correlated with metabolic risk scores nor affected the WC effects on insulin resistance and metabolic risk scores in the GLM. CONCLUSIONS: Postmenopausal Chinese women with abdominal obesity may carry higher metabolic cardiovascular risk than those without it. It is WC, not BMI, that predicts metabolic cardiovascular risk factors in these women.

Abdomen↗

PubMedDate not supplied

Quantitative vibration perception thresholds in normal and diabetic chinese: influence of age, height and body mass index.

In this study, we established normality data of vibration perception thresholds (VPT) in a Chinese population. Over 1,400 healthy subjects were recruited to create age-related centile charts of VPT after pretesting for reliability. Another 273 diabetic (DM) patients were recruited to assess the impact of age, height and body mass index (BMI) on VPT values in DM and non-DM subjects. The present study is the first one which reports normality data of VPT from a large Chinese population. The VPT values were higher in male and female DM patients than in the non-DM counterparts. Age significantly contributed to the variance of VPT in both DM and non-DM subjects. Height was positively associated with VPT in men, so was BMI in non-DM subjects with much smaller magnitudes of effect than for age.

Adult↗