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Biomedical subjects

M S Kumar

Publications and source records attributed to M S Kumar.

At least 109 records · Page 6Linked to original sources
PubMed1984

Effect of short photoperiod on hypothalamic methionine-enkephalin and LHRH content and serum beta-endorphin-like immunoreactivity (beta-end LI) levels in golden hamsters.

Adult female golden hamsters were used to study the effect of short photoperiod on the endogenous opioid system and the effect of pinealectomy on the serum beta-endorphin-like immunoreactivity (beta-end LI) levels. Hamsters were housed under either long photoperiod (14L:10D) or short photoperiod (2L:22D) and the regularity of the estrous cycles was determined by daily vaginal exfoliative cytology. Hamsters under short photoperiod became acyclic after about 7 wk. At the end of 8 wk, all the hamsters were decapitated and medial basal hypothalamic (MBH) content of LHRH and methionine-enkephalin (met-enkephalin) were measured by specific radioimmunoassays (RIA). Both LHRH and met-enkephalin levels of the MBH were significantly elevated in the short-photoperiod hamsters as compared to the normally cycling control animals under long photoperiod. In a second experiment, the effect of pinealectomy (PNX) on the serum levels of beta-end LI in the short-photoperiod hamsters was determined. The serum beta-end LI levels were increased approximately threefold in the noncyclic hamsters housed under 8 wk of short-photoperiod conditions. Pinealectomized hamsters kept under 8 wk of short-photoperiod exhibited lower serum beta-end LI levels similar to those of normally cycling hamsters kept under long photoperiod. These results indicate a possible functional relationship between increased pineal activity (as a result of short photoperiod) and increased MBH met-enkephalin, LHRH, and serum beta-end LI levels.

Animals↗
PubMed1984

Effect of chronic administration of delta 9-tetrahydrocannabinol on the endogenous opioid peptide and catecholamine levels in the diencephalon and plasma of the rat.

The effect of chronic administration of delta 9-tetrahydrocannabinol (delta 9-THC) on the endogenous opiate and catecholamine levels was investigated. Intact male rats were injected daily either with vehicle (50 microliters oil) or delta 9-THC in oil (3 mg delta 9-THC/kg body wt). The treatments were administered subcutaneously over a period of 25 days. All animals were decapitated after the last injection and trunk plasma was assayed for prolactin, beta-endorphin-like immunoreactivity (beta-end LI), norepinephrine (NE), epinephrine (E), dihydroxyphenyl acetic acid (DOPAC) and dopamine (DA). The preoptic area (POA) and medial basal hypothalamus were assayed for methionine enkephalin, beta-endorphin and catecholamines. Chronic delta 9-THC treatment resulted in an increase in POA and MBH methioine-enkephalin and beta-end LI as well as an increase in plasma beta-end LI. The POA, MBH and plasma NE and E levels were lower in these animals when compared with the controls. In the MBH, however, the delta 9-THC treated rats contained higher DA and DOPAC levels when compared with the controls. These results support our view that chronic delta 9-THC administration alters the activities of the endogenous opiate system as well as the catecholaminergic system and consequently impairs the endocrine functions.

Animals↗
PubMed1983

Effect of an acute dose of delta 9-THC on hypothalamic luteinizing hormone releasing hormone and met-enkephalin content and serum levels of testosterone and corticosterone in rats.

The effects of delta 9-tetrahydrocannabinol (delta 9-THC) on endocrine responses of ovariectomized rats and intact male rats were investigated. In delta 9-THC treated ovariectomized rats, the mediobasal hypothalamic (MBH) LHRH and methionine-enkephalin (met-enk) contents were high compared to either vehicle or naloxone groups. However, delta 9-THC, when administered simultaneously with naloxone, failed to change MBH LHRH levels in the ovariectomized rats. This suggests that LHRH release from the MBH, which is normally accelerated by ovariectomy, is blocked by delta 9-THC and this inhibitory effect of delta 9-THC on LHRH release is reversed by naloxone, suggesting an involvement of endogenous opiate system. In a second experiment using intact male rats, delta 9-THC was administered at 2 mg, 15 mg, and 30 mg/kg body weight. The delta 9-THC decreased immunoassayable LHRH in anterior hypothalamus preoptic area (AHPOA) and MBH in a dose-related manner. Significant increases in serum corticosterone and decreases in serum testosterone were also observed in the rats due to delta 9-THC treatment. The met-enk content of AHPOA and MBH was significantly increased in delta 9-treated rats. The results of this study suggest that delta 9-THC may decrease biosynthesis and/or release of LHRH by partly interacting with the endogenous opiate system.

Animals↗
PubMed1983

Naloxone blocks the effects of delta 9-tetrahydrocannabinol on serum luteinizing hormone and prolactin in rats.

The present study was undertaken to determine if the effects of delta 9-tetrahydrocannabinol on gonadotropin secretion are mediated through endogenous opioid neurons in the rat. Ovariectomized rats were treated with estradiol-benzoate (EB, day O) and with progesterone (P) at 11:00 h on day 2. At 13:00 h (day 2), these estradiol primed and progesterone-treated (EBP) animals received either delta 9-THC (3mg/kg in oil, i.m.); naloxone (Nal) 3 mg/kg in saline, s.c.) or delta 9-THC + Nal. All animals were decapitated at 16:00 h and trunk sera were assayed for luteinizing hormone (LH) and prolactin (Prl), while medial basal hypothalami (MBH) were assayed for luteinizing hormone-releasing hormone (LHRH). Naloxone enhanced the EBP-induced hypersecretion of LH by 2-fold while delta 9-THC completely blocked the EBP-induced secretion of LH. delta 9-THC slightly diminished the stimulatory effect of Nal on LH secretion and caused a 2-fold increase in serum Prl concentrations, while Nal did not influence the serum PRL levels in these EBP rats. However, Nal did block the stimulatory effects of delta 9-THC on Prl secretion. delta 9-THC caused a significant increase in MBH content of LHRH, an effect which was prevented by Nal. These results suggest that the inhibitory effects of delta 9-THC on serum LH and the stimulatory effect of the cannabinoid on Prl are mediated by an opioid mechanism.

Animals↗
PubMed1982

Altered hypothalamic dopamine depletion rate and LHRH content in noncyclic hamsters.

Effect of light deprivation on hypothalamic dopamine (DA) depletion rate and luteinizing hormone releasing hormone (LHRH) content was evaluated in golden hamsters. Hamsters maintained in continuous darkness (CD) became acyclic after about 6 weeks while another group of hamsters maintained vaginal cyclicity under 20 lux light intensity for 14 hours a day. All hamsters were ovariectomized subsequently. Luteinizing hormone releasing hormone levels were significantly higher in the medial basal hypothalamus (MBH) and the serum gonadotropin levels were significantly lower in CD hamsters when compared with 20 lux group. However, gonadotropin release in response to exogenous LHRH was not significantly different in CD or 20 lux group of hamsters. Examination of hypothalamic catecholamine levels one hour after alpha-methyl-p-tyrosine injection indicated that the DA depletion was higher in CD animals. Results indicate that light deprivation probably enhances DA depletion rate in the MBH, suggesting that increased activity in dopaminergic neurons may inhibit the release of MBH LHRH in hamsters kept in continuous darkness.

Animals↗
PubMed1982

Diurnal fluctuations in methionine-enkephalin levels in the hypothalamus and preoptic area of the male rat: effects of pinealectomy.

Methionine-enkephalin (met-enk) levels were measured at 09.30-10.30, 16.30-17.30 and 23.30-00.30 h in the anterior hypothalamus-preoptic area (AHPOA), medial basal hypothalamus (MBH), anterior, intermediate and posterior lobe of the pituitary gland of male rats. Met-enk levels in the AHPOA and MBH fluctuated significantly through a 24-hour period; from low levels at 09.30-10.30 h, met-enk in the AHPOA and MBH rose slowly in the afternoon to reach peak concentrations at 23.30-00.30 h. Pinealectomy appears to depress or shift the normally occurring increments in met-enk levels at 23.30-00.30 h in the AHPOA only. Serum testosterone (T) levels displayed an inverse relationship with the met-enk rhythm; high concentrations during the day were associated with low met-enk levels and as T levels decreased to a nadir at 23.30-00.30 h, the met-enk in the MBH and AHPOA attained peak concentrations. Daily changes in serum T levels were not affected by pinealectomy.

Animals↗
PubMed1981

Diagnosis of self-induced hyperinsulinism in an insulin-dependent diabetic patient by radioimmunoassay of free C-peptide.

On the basis of results of simultaneous determinations of plasma free insulin and free c-peptide, episodes of hypoglycemia in an insulin-dependent diabetic were attributed to surreptitious self-administration of insulin. Immunoreactive c-peptide values were falsely increased and diagnostically misleading when measured in unextracted plasma. After preliminary removal of antigen/antibody complexes from the plasma by extraction with polyethylene glycol, the c-peptide values, referred to as "free c-peptide," were suppressed. We suggest that insulin antibodies formed complexes with proinsulin-like material in the plasma of this patient, which accounted for most of the c-peptide immunoreactivity in her unextracted plasma. These complexes must be removed if c-peptide measurements are to be accurate.

Adolescent↗
PubMed1980

Measurement of serum C-peptide immunoreactivity by radioimmunoassay in insulin-dependent diabetics.

A radioimmunoassay for C-peptide utilizing synthetic C-peptide as an antigen and tyrosylated synthetic C-peptide for iodination was evaluated for its clinical use. Mean fasting C-peptide levels in 24 normal subjects was 2.6 +/- 0.8 ng/ml. During the oral glucose tolerance test, baseline C-peptide in five normal subjects was 1.5 +/- 0.8 ng/ml, and at 60 min was 5.6 +/- 1.6 ng/ml. For two insulin-dependent diabetic patients, diagnoses of factitious hypoglycemia were documented on the basis of simultaneous free insulin and C-peptide determinations. Sera from 24 insulin-dependent diabetics were analyzed for free and total immunoreactive C-peptide and insulin levels. For 20% of juvenile and 64% of maturity-onset diabetics, the presence of proinsulin-like material bound to insulin antibodies was demonstrated by measurement in unextracted serum. This accounted for 20% to 100% of total C-peptide immunoreactivity in these patients. Simple polyethylene glycol precipitation of immune complexes and the measurement of free immunoreactive C-peptide in the supernatant demonstrated subnormal levels (less than 0.5 ng/ml) in all juvenile diabetics and normal levels (1.8 +/- 1.3 ng/ml) in 70% of maturity-onset diabetics.

Adolescent↗
PubMed1980

Distribution of luteinizing hormone releasing hormone in the canine hypothalamus: effect of castration and exogenous gonadal steroids.

The effect of exogenous gonadal steroids or orchidectomy on the distribution and concentration of luteinizing hormone-releasing hormone (LHRH) in the hypothalamus of the dog was studied. Various hypothalamic area of the canine brain were extracted with 90% methanol and processed, and LHRH was assayed, using a specific radioimmunoassay. The highest concentration of immunoreactive LHRH was found in the infundibular, premammillary, preoptic, and suprachiasmatic areas in intact dogs. Measurable amounts of LHRH were found in the mammillary and lateral hypothalamic regions. The hypothalamus in the male dog had significantly (P < 0.05) higher LHRH concentrations 3 mm lateral to the midsagittal line (the lateral hypothalamic area) as compared with the area in the anestrous female dog. Daily estrogen treatment of female dogs with 0.2 mg/day or 1 mg/day, IM, or with testosterone propionate (1 mg/day, IM) for 3 weeks increased LHRH concentration 2.5- to 5-fold in the mammillary, premammillary, and infundibular areas and almost 40-fold in the preoptic, rostral commissural area and in the lateral and dorsal hypothalamic regions. Orchidectomy caused an increase in LHRH concentration in the preoptic and suprachiasmatic area with a concurrent decrease in LHRH in the infundibular area. Therefore, in the dog, LHRH is possibly synthesized or transported (or both) from different regions of the hypothalamus to the median eminence, and the gonadal steroid feedback mechanism is complex, involving multiple sites of action in the hypothalamus and the components of the limbic system.

Animals↗
PubMed1979

Enhancing effect of thyroxine on tumor growth and metastases in syngeneic mouse tumor systems.

We studied the effect of thyroxine treatment on tumor growth and metastases resulting from tumor implants on the hind feet of mice in two syngeneic systems. In control, untreated A/Jax mice, tumor Sarcoma 1 at Day 14 after implantation had average tumor weight of 582 +/- 60 (S.D.) mg and showed an incidence of 57% metastases to regional popliteal nodes and 5% metastases to thymus. In contrast, the thyroxine-treated group (40 microgram/mouse s.c., 5 times/week for 1 month) had an average tumor weight of 808 +/- 56 mg (p less than 0.001), and metastases to popliteal nodes and thymus were 90 and 35%, respectively. In another syngeneic tumor system, Lewis fibrosarcoma was implanted in C57BL/6J mice, and the tumor weight and metastatic index (derived from the number and size of the pulmonary tumor foci) were determined at Day 28. Again, the synthetic L-thyroxine treated group showed a significant enhancement tumor growth and metastatic index. The mean tumor weight in the treated group was 385 +/- 26 mg (control, 694 +/- 25 mg; p less than 0.005) and metastatic index was 84 +/- 29 (control, 30 +/- 25; p less than 0.001). Induced hypothyroidism (treatment with 131I, 100 microCi/mouse i.p.) showed the reverse effect on both tumor systems. These results suggest that both tumor systems are dependent on thyroid hormones for their growth and spread.

Animals↗
PubMed1979

Isolation and partial characterization of prolactin from equine pituitary gland (hypophysis).

Highly purified equine prolactin was prepared from equine pituitary glands (hypophysis) by serial extractions with water at pH 5.5, 0.1 M (NH4)2SO4 at pH 4.0, and 0.25 M (NH4)2SO4 at pH 5.5 to remove other hormones, and then finally with 70% ethanol at pH 9.3 to 10.0 to extract prolactin. Preliminary purification of the extract involved salting out other substances with 0.1% NaCl at pH 9.0. Prolactin was precipitated out by adding three times the volume of 95% ethanol at 4 C. This prolactin preparation had a biological potency of 24 IU/mg. Further purification by isoelectric focusing on a pH gradient of 5 to 7 gave three prolactin components with the following characteristics: isoelectric point 5.8, 5.7, and 5.25; biological potencies (IU/mg) 35.6, 19.6, and 11.3. The major component had a molecular weight of 25,000, an isoelectric point of 5.8, and a biological potency of 35.6 IU/mg. Antiserum produced against this component did not cross-react with equine follicular stimulating hormone, luteinizing hormone, and growth hormone, but did cross-react with ovine and bovine prolactin. Human and murine prolactin had little cross-reactivity with the equine prolactin antiserum.

Animals↗
PubMed1979

Improved indirect and direct radioimmunoassay for carcinoembryonic antigen.

Values obtained by the indirect and the direct assays for carcinoembryonic antigen by use of the "CEA Roche" method and reagents differ significantly. In 32 samples the latter method gave values almost twofold those obtained by the former. The mean ratio for direct/indirect was 1.9 +/- 0.6. Analytical recovery experiments on samples to which known amounts of the antigen had been added showed a similar disparity. A simple modification of these two procedures, involving addition of normal human plasma (containing less than 2.0 microgram of the antigen per liter) to standards, eliminated this discrepancy. In the indirect method, standards were added to normal human plasma, then extracted with perchloric acid before assay. In the direct assay normal human plasma instead of goat serum, was added to standards. With these modifications the analytical recoveries of added CEA by the indirect and direct methods were 87 +/- 17% and 99.7 +/- 8%, respectively, and the mean ratio between two methods was 1.2 +/- 0.4.

Animals↗