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Biomedical subjects

I Khan

Publications and source records attributed to I Khan.

At least 181 records · Page 10Linked to original sources
PubMed1985

Influence of high-density lipoprotein on estradiol stimulation of luteal steroidogenesis.

The aim of this investigation was to determine whether luteal cells utilize cholesterol derived from high-density lipoprotein (HDL) for steroidogenesis and whether estrogen enhances luteal utilization of exogenous sterol. Incubation of Day 15 corpora lutea (CL) with different doses of human HDL resulted in a dose-dependent increase in progesterone production. HDL in vitro enhanced the overall steroidogenic capacity. However, the percentage of increases in 17 alpha-hydroxyprogesterone, testosterone and estradiol were significantly less than that of progesterone. Day 12 hypophysectomized and hysterectomized pregnant rats were treated with either estradiol, testosterone or vehicle for 72 h. Serum pregnenolone and progesterone were markedly increased by the steroid treatment, yet in vitro production of progesterone by CL in all the groups was similar. However, in the presence of HDL in the media, only luteal tissues from steroid-treated rats increased their progesterone output. The reduced production of progesterone by luteal cells of vehicle-treated rats was not due to an accumulation of pregnenolone but to an overall reduction in exogenous sterol utilization. In summary, results of this investigation suggest 1) luteal cells of pregnant rats effectively utilize cholesterol from HDL for maximal steroidogenesis, and 2) estradiol may stimulate luteal steroidogenesis, at least in part, by affecting the incorporation or utilization of cholesterol from HDL into the cell.

17-alpha-Hydroxyprogesterone↗
PubMed1985

Regulation of luteal cell 3-hydroxy-3-methylglutaryl coenzyme A reductase activity by estradiol.

Recent studies have suggested that estradiol or androgen precursor may stimulate steroidogenesis in the luteal cell by modulating intracellular sterol availability and metabolism. This investigation was performed to examine the effect of estradiol on de novo synthesis of cholesterol. Pregnant rats hypophysectomized and hysterectomized on Day 12 were treated for 72 h with either estradiol or testosterone. De novo cholesterol synthesis was determined by measurement of the specific activity of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, the rate limiting enzyme in cholesterol biosynthesis, in microsome-enriched preparations of luteal tissue and incorporation of [14C] acetate into cholesterol by corpora lutea incubated in vitro. Estradiol or testosterone treatment caused a 4- to 5-fold stimulation of luteal cholesterol biosynthesis, as measured by these techniques. NaF, an inhibitor of phosphatase which blocks the conversion of the inactive enzyme to the active form, reduced the HMG CoA reductase activity to 30% in corpora lutea obtained from either steroid or vehicle-treated rats. However, an increase in enzyme activity of comparable magnitude by steroids was observed whether microsomes were isolated with or without NaF. The effect of estradiol appears to be enzyme-specific, since it failed to affect the microsomal marker, NADPH-cytochrome c reductase. Since the cholesteryl ester content of corpora lutea falls in response to steroid treatment, rats were treated with 4-aminopyrazolo-[3,4d]pyrimidine (4-APP) to deplete cellular cholesterol content.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine↗
PubMed1984

Biological activity of the alkaloids of Erythroxylum coca and Erythroxylum novogranatense.

The cultivated Erythroxylum varieties E. coca var. coca, E. coca var. ipadu, E. novogranatense var. novogranatense and E. novogranatense var. truxillense contain 18 alkaloids, identified so far, belonging to the tropanes, pyrrolidines and pyridines, with cocaine as the main alkaloid. The biological activity of the following alkaloids has been reported in the literature: cocaine, cinnamoylcocaine, benzoylecgonine, methylecgonine, pseudotropine, benzoyltropine, tropacocaine, alpha- and beta-truxilline, hygrine, cuscohygrine and nicotine. The biological activity of cocaine and nicotine is not reviewed here, because it is discussed elsewhere in the literature. Hardly anything is known about the biological activity of the other alkaloids present in the four varieties mentioned. The biosynthesis of the coca alkaloids has been outlined.

Alkaloids↗
PubMed1984

Regulation of luteal cell lipoprotein receptors, sterol contents, and steroidogenesis by estradiol in the pregnant rat.

Although estradiol has been found to possess receptors in the luteal cell and to stimulate progesterone synthesis, its mechanism of action in the corpus luteum remains completely unknown. To determine whether estradiol modulates cellular uptake of lipoprotein substrate and intracellular cholesterol utilization, pregnant rats were hypophysectomized and hysterectomized on day 12 to reduce the luteal content of estradiol. They were treated with either 100 micrograms estradiol daily or with a 1-cm capsule filled with testosterone, which maintained luteal estradiol at levels found in intact pregnant rats. Blood was obtained 24, 48, and 72 h later for progesterone and cholesterol measurement. At 72 h, rats were killed, and corpora lutea (CL) were isolated for measurement of cholesteryl ester, free cholesterol, and [125I]iodo high density lipoprotein [( 125I]iodo-HDL)- and [125I]iodo-hCG-binding activities. In vivo treatment with estradiol or testosterone increased serum progesterone concentrations from 35 +/- 7 ng/ml in vehicle-treated rats to 128 +/- 21 and 118 +/- 16, respectively, and luteal weight from 2.1 +/- 0.2 mg/CL to 3.9 +/- 0.3 and 4.0 +/- 0.3 within 72 h. However, steroid treatment did not induce a change in luteal cell number, since the content of DNA per CL remained similar in all groups. It also did not modify levels of serum cholesterol. [125I]Iodo-HDL binding in luteal cells increased from 3.2 +/- 0.3 pg/cell in vehicle-treated rats to 9.9 +/- 0.8 and 7.9 +/- 0.6 after estradiol or testosterone treatment, while the luteal cell content of cholesteryl ester declined from 12.5 +/- 2.0 to 7.7 +/- 0.5 and 8.4 +/- 0.9 micrograms/CL, respectively. Thus, estradiol or testosterone increases luteal cell size but not cell number, depletes cholesteryl ester, and enhances HDL receptor content and progesterone synthesis. These results suggest that one possible mechanism by which estradiol and testosterone stimulate luteal cell steroidogenesis is by increasing the delivery of cholesterol substrate through a receptor-mediated process and by enhancing cholesterol utilization.

Animals↗
PubMed1984

Khat: an amphetamine-like plant material.

The chewing of leaves of the khat shrub is common in certain countries of East Africa and the Arabian peninsula, and many khat users are subject to psychic dependence on the drug. The syndrome observed after khat consumption is characterized by a certain degree of CNS stimulation and by sympathomimetic effects; it is reminiscent of that induced by amphetamine.Recently, the alkaloid (-)-cathinone has been isolated from khat leaves and this substance produces effects in animals that are analogous to those of (+)-amphetamine and that correlate well with the effects observed in humans after khat consumption. Furthermore, it has been shown that (-)-cathinone acts by the same mechanism as (+)-amphetamine, i.e., by inducing release at physiological catecholamine storage sites. Taken together, these studies indicate that khat must be considered an amphetamine-like material.

Alkaloids↗
PubMed1983

Benzodiazepine receptors in fish brain: [3H]-flunitrazepam binding and modulatory effects of GABA in rainbow trout.

We have identified and partially characterised benzodiazepine binding sites in whole brain membranes of male rainbow trout. In terms of Bmax and KD values trout brain receptors are remarkably similar to those in rat and human brain. The Hill coefficient was 0.98, indicating a single binding site. GABA (10(-4) M) was able to significantly elevate binding of [3H]-FNZ through a change in KD rather than Bmax. This effect was prevented by the GABA receptor antagonist bicuculline methiodide.

Animals↗
PubMed1983

Tuberculous granuloma of the epiglottis.

A case of tuberculous granuloma of the epiglottis is presented. The presenting symptoms were hoarseness and painful dysphagia, and the laryngoscopic appearances resembled carcinoma. Histological examination of the biopsy material was diagnostic, emphasising the difficulty of diagnosis in the general population.

Epiglottis↗
PubMed1982

beta-Adrenergic, but not benzodiazepine, binding sites are reduced in dystrophic mouse brain.

We have examined brain tissue from dystrophic mice (male 129/ReJ-dy and female 129 B6F1/J-dy) to determine whether CNS lesions may accompany the known muscular defects. In all brain regions examined we found a significant reduction in the numbers of beta-adrenergic binding sites when compared to brain from control mice. In contrast, the number of benzodiazepine binding sites appeared normal. These changes in adrenergic sites may be related to the known abnormally high excretion of catecholamines. Our results also emphasise the need to study extra-muscular sites in this disease.

Animals↗
PubMed1981

Different patterns of cyclic AMP accumulation in rat corpora lutea after LH stimulation in vitro and in vivo.

Tissue levels of cyclic AMP were measured in rat corpora lutea at various times after administration of LH in vitro and in vivo. In-vitro addition of LH produced more pronounced accumulation of cyclic AMP in very young corpora lutea (1-day-old) than in the older corpora lutea (3- and 7-day-old). When LH was administered in vivo the highest accumulation of cyclic AMP was seen in the older corpora lutea (7- and 3-day-old).

Animals↗