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Biomedical subjects

N Parvizi

Publications and source records attributed to N Parvizi.

68 records · Page 4Linked to original sources
PubMed1977

Gonadotrophin secretion in the ovariectomized guinea-pig: effects of electrical stimulation of the hypothalamus and of LH-RH.

1. Serial blood samples were collected from anaesthetized spayed guinea-pigs subjected to anterior hypothalamic stimulation or injected with luteinizing hormone-releasing hormone (LH-RH), and the effect on the secretion of follicle-stimulating hormone (FSH) and LH followed. 2. Hypothalamic stimulation enhanced LH secretion, although the response waned during the course of the 1 hr period of stimulation; the secretion of FSH was not increased. After stimulation, FSH and LH levels fell below control values. 3. The response to stimulation of the hypothalamus was greater 2 weeks after spaying than after 1 week. 4. Since repeated periods of hypothalamic stimulation induced repeated surges of LH secretion, the decline in LH secretion during stimulation was not likely to have resulted from hypothalamic damage, while the observation that the plasma concentration of FSH and LH declined below control values after brain stimulation implies the operation of inhibitory mechanisms. 5. Pre-treatment of spayed guinea-pigs with progesterone depressed the resting plasma concentration of LH but did not affect the immediate response to hypothalamic stimulation. After hypothalamic stimulation the plasma gonadotrophin levels did not fall below control values. 6. Pre-treatment with oestradiol benzoate depressed the resting plasma level of LH and slightly reduced the size of the LH surge produced by hypothalamic stimulation. However, the raised plasma LH concentration was sustained after stimulation ended. 7. The response to hypothalamic stimulation after pre-treatment with progesterone and oestradiol benzoate showed features of the reaction to each steroid given singly. 8. The I.V. injection of 0-5 microng LH-RH induced a surge of LH secretions without affecting FSH discharge. 9. Pre-treatment with progesterone did not greatly modify the response to LH-RH but after an injection of oestradiol the high level of LH produced by the releasing factor was sustained for about 2 hr. 10. Injections of LH-RH during the phase of depressed LH release after hypothalamic stimulation produced a surge of LH secretion which matched that seen in non-stimulated animals.

Animals↗
PubMed1976

Plasma luteinizing hormone and progesterone in the adult female pig during the oestrous cycles, late pregnancy and lactation, and after ovariectomy and pentobarbitone treatment.

In a series of experiments on female miniature pigs, the pattern of plasma LH and progesterone levels during the oestrous cycle, late pregnancy and lactation and after ovariectomy were characterized, and the effect of pentobarbitone treatment was tested. The preovulatory surge of LH occurred in seven out of eight animals between 00.00 and 12.0 h on day 0 of the oestrous cycle (day 1 of standing heat). Plasma progesterone strated to decline 8 days before oestrus and reached its lowest value 5 days before the preovulatory LH peak. Increases in progesteron concentration were already noticeable 48 h after the LH surge. During late pregnancy, parturition and lactation, plasma LH was low and showed only minor fluctuations, while plasma progesterone declined 4 to 5 days before parturition. Both hormones remained at low levels throughout lactation. Three weeks before parturition increases in LH were always followed by an increase in progesterone. This dependency was greatly diminished immediately before delivery. Four to 12 days after weaning the animals came into oestrus which was followed by an increase in LH and later an increase in progesterone concentrations. Ovariectomy during dioestrus resulted in a steady increase in plasma LH levels of 35-39 days. Ovariectomy caused abortion if performed on day 100 of pregnancy. It was followed by a rapid increase of plasma LH concentration. Normal parturition (around day 115) and lactation took place when animals were spayed on day 112 of pregnancy. In this case, plasma LH levels remained even lower than before ovariectomy as long as lactation was maintained. Immediately after weaning a rapid increase in the normal postovariectomy pattern of LH secretion was observed. Pentobarbitone anaesthesia (30-35 mg/kg body wt, initial dose), during pro-oestrusoestrus, for less than 5 h had no effect on the preovulatory LH increase. However, pentobarbitone anaesthesia for more than 6 h inhibitied the LH peak and ovulation if the animal was under deep anaesthesia before 24.00 h on the day before oestrus. Pentobarbitone treatment of ovariectomized pigs resulted in a clear decrease in LH levels 40 min after a single i.v. dose.

Animals↗
PubMed1975

Plasma luteinizing hormone and testosterone in the adult male pig: 24 hour fluctuations and the effect of copulation.

Secretory patterns of LH and testosterone were characterized in the intact male miniature pig. All blood samples were taken from indwelling catheters. Hourly sampling was carried out over 24 h and during a morning period blood was collected for 2 h at 10 min intervals. No significant difference was detected in the plasma LH concentration on the basis of hourly sampling. Plasma testosterone was significantly (P less than 0-05) lower during the evening and night when compared with morning values. The second experiment was concerned with the pattern of plasma LH and testosterone concentrations before and after copulation. Blood sampling was performed at 10 min intervals. Plasma LH was significantly (P less than 0-001) raised for 30 min after copulation when compared with any 30 min period (0-120 min) before copulation. Plasma testosterone was not significantly altered for any 30 min period of the experiment (0-270 min). The data are interpreted as a possible mechanism for endocrine control of testicular function.

Animals↗