Biomedical subjects

S Mansfield

Publications and source records attributed to S Mansfield.

27 records · Page 2Linked to original sources

PubMed1985

Central opioids: a possible role in parturition?

Pregnant rats were implanted with subcutaneous minipumps to deliver either naloxone or saline. The time-course of subsequent parturition was different between the two groups: the interval between successive births was significantly shorter for the naloxone-treated rats. This supports the hypothesis that the opioid innervation of the neurohypophysis, which is known to influence oxytocin release profoundly, has a physiological role in parturition. To test the further hypothesis that this role is particularly important in a stressful environment, pregnant rats, again implanted with minipumps, were regularly transferred, at 15-min intervals beginning with the birth of the first pup, between their normal cage and the unfamiliar environment of a glass observation chamber. No difference was noted between the time-courses of parturition for the naloxone- and saline-treated groups, although the time-courses were markedly altered from those observed in rats not subjected to an unfamiliar environment. We conclude that opioid modulation of oxytocin release may play a role in 'spacing' the delivery of successive births during normal parturition.

Animals↗

PubMed1984

Relative effectiveness of naloxone and MR2266 in potentiating oestrogen-stimulated luteinizing hormone surges in ovariectomized female rats.

The oestrogen-stimulated surge of luteinizing hormone (LH) can be inhibited by opiates and potentiated when endogenous opiate pathways are blocked by naloxone. Experiments were undertaken to allow an assessment to be made of the opiate receptor category predominantly responsible for inhibiting LH secretion. Thus the effects of MR2266 (primarily a mu and kappa antagonist) and naloxone (primarily a mu and delta antagonist) on LH surges were compared. At a dose of 4.5 mg/kg, administered three times in the 6 h preceding the LH surge, naloxone significantly potentiated LH release whereas this dose of MR2266 was without effect. However at the lower dose of 0.5 mg/kg, administered three times also, the size of the LH surge was significantly increased by MR2266 but not by naloxone.

Animals↗

PubMed1984

Anaesthesia with alphaxalone plus alphadolone acetate blocks the oestrogen-stimulated LH surge and impairs pulsatile LH secretion in ovariectomized female rats.

Two experiments were undertaken to assess further the action of the steroid anaesthetic alphaxalone upon LH secretion in chronically ovariectomized female rats. For the first experiment, 31 rats were given two injections of oestradiol benzoate (20 micrograms/100 g body weight), each 72 h apart, to stimulate an LH surge 6 h after the second injection. However, one group of seven rats was anaesthetized with alphaxalone throughout the 6-h period and a second group of eight was similarly anaesthetized only for the last 2 h of the 6-h period. The steroid-stimulated LH surge was blocked in both groups of rats anaesthetized with alphaxalone. The second experiment involved a comparison of pulsatile LH secretion in animals which were either unanaesthetized (n = 8) or anaesthetized with alpha xalone (n = 9). In six out of nine rats the anaesthetic did not affect the maximum or minimum plasma LH concentrations but significantly slowed the frequency at which LH pulses were measured. In the remaining three anaesthetized rats the drug blocked pulsatile LH secretion. The experiments confirm that some secretion of LH continues during alphaxalone anaesthesia but indicate also that the drug has a more deleterious action upon the oestrogen-stimulated LH surge than believed hitherto.

Anesthetics↗

PubMed1983

Elevation of circulating prolactin concentrations may not cause striatal dopamine receptor supersensitivity.

Neuroleptic drugs, on repeated administration, increase plasma prolactin levels and induce behavioural and biochemical changes suggesting supersensitivity of striatal dopamine receptors. It has been suggested that the increase in plasma prolactin is responsible for the change in striatal dopamine receptors. We now find that repeated administration of haloperidol (5 mg/kg i.p.) for 21 days, followed by a 3 day drug-washout period, caused a 12-fold increase in circulating prolactin concentration in samples taken 1 h after the last injection. Haloperidol treated animals also exhibited an exaggerated stereotyped response to apomorphine 0.0625-0.5 mg/kg s.c.) and an increase in striatal dopamine receptor numbers labelled by [3H]spiperone. Administration of the same dose of domperidone or sulpiride (5 mg/kg i.p., 21 days), compounds which penetrate poorly into brain, also elevated plasma prolactin levels, but failed to alter cerebral dopamine function. Our findings indicate that neuroleptic-induced elevations in plasma prolactin levels are not responsible for the induction of cerebral dopaminergic supersensitivity.

Animals↗

PubMed1981

Secretion of luteinizing hormone in ovariectomized adult rats treated neonatally with monosodium glutamate.

We have studied the possible effects of monosodium glutamate (MSG) on LH secretion in ovariectomized rats. In experiment 1 MSG-treated and control rats were given oestradiol benzoate at noon and 72 h later half the rats in each group were given a second injection of oestradiol benzoate or progesterone. Blood samples were taken immediately before and 6 h after these i.m. injections. At 78 h there were no significant differences in plasma LH concentration measured in the two groups of rats given progesterone or in the two groups given a second injection of oestradiol benzoate although for both MSG-treated and control rats progesterone produced a significantly (P less than 0.01) greater LH surge than did oestradiol benzoate. In experiment 2 100 ul blood samples were collected at 5-min intervals for up to 3 h from MSG-treated and control rats. For rats showing more than one pulsatile discharge of LH, peak and trough values for plasma LH concentrations were no significantly influenced by MSG treatment. However the mean pulse height was significantly (P less than 0.001) greater in the MSG-treated group than in control rats. Pulsatile release stopped more quickly in the MSG-treated rats and their mean plasma LH concentration after 120 min of blood sampling was significantly (P less than 0.05) lower than that obtained in the control animals. Thus, although some aspects of LH secretion seem to be significantly different in MSG-treated rats, these effects may result from the greater sensitivity of the MSG-treated animals to experimental manipulation.

Animals↗

PubMed1980

Discharge of gonadotrophin-releasing hormone from the mediobasal part of the hypothalamus: effect of stimulation frequency and gonadal steroids.

The release of gonadotrophin-releasing hormone (Gn-RH), in response to electrical stimulation of the mediobasal part of the hypothalamus incubated in vitro, was studied in both male and female rats. In male rats significant release of Gn-RH occurred during the 10-min experimental period only when the incubated tissue was stimulated at frequencies of 10 Hz or greater. There was no release when stimulated at 5 Hz. There was also no release of hormone when the mediobasal hypothalami were incubated in a Ca2+ free medium. The amount of Gn-RH released during a 10-min incubation period increased progressively as the frequency of stimulation was raised from 10--100 Hz. During short (4-min) incubation periods the effectiveness of each stimulus pulse for Gn-RH release also increased with the frequency of stimulation. However, when stimulated for 10 min there was no increase in hormone released per stimulus pulse when frequency of stimulation was raised above 10 Hz. The amount of Gn-RH released in response to stimulation at 50 Hz was greater in male rats than in females. For the females, there was no significant difference between the amounts of Gn-RH released at dioestrus and pro-oestrus. In both male and female rats gonadectomised 4 weeks prior to hypothalamic incubation, the response to electrical stimulation at 50 Hz was reduced when compared with intact controls. Indeed, for the females there was no longer a statistically significant increase in the amount of Gn-RH in the incubation medium after 50 Hz stimulation. Ovariectomised female rats, injected twice daily for 3.5 days with 20 microgram of oestradiol benzoate released Gn-RH in response to 50 Hz stimulation in the same amounts as intact control animals. By contrast, there was no recovery of Gn-RH release to normal levels in castrated male rats similarly treated with 1.25 mg testosterone propionate.

Animals↗

PubMed1980

Relationship between duration of urethane or pentobarbitone anaesthesia in male and female rats and adenohypophyseal response to luteinising hormone-releasing hormone.

1 Luteinizing hormone releasing hormone (50 ng/100 g body weight) was injected into male and female rats which had been anaesthetized with either urethane (1.2 g/kg) or pentobarbitone (45 g/kg) for 15, 100 or 240 min and serial blood samples were taken for estimation of plasma luteinizing hormone concentrations. 2 The rats anaesthetized with urethane tended to show a greater response to the releasing hormone than those given pentobarbitone. 3 The magnitude of the responses observed in male rats and in female rats anaesthetized with pentobarbitone did not change as the period of anaesthesia prior to injection of releasing hormone was lengthened from 15 min to 4 h. By contrast, in the groups of female rats anaesthetized with urethane the magnitude of the response to luteinizing hormone releasing hormone was related to the length of pretreatment anaesthesia. Thus both dioestrous and pro-oestrous rats given releasing hormone only 15 min after the onset of urethane anaesthesia had significantly (P less than 0.001 and less than 0.05 respectively) higher concentrations of luteinizing hormone (LH) in the plasma than rats treated with the releasing hormone after 240 min of anaesthesia. 4 These effects were not due to a differential action of the anaesthetics on the mechanism for clearing LH from the plasma.

Anesthesia↗

PubMedDate not supplied

AIDS and palliative care.

Explore the source record for details and available documents.

Acquired Immunodeficiency Syndrome↗

PubMedDate not supplied

Subcutaneous fluid administration and site maintenance.

As nurses working with older patients, the authors noticed a marked increase in the use of subcutaneous fluid administration as an alternative to the more traditional intravenous route, as a means of managing hydration in certain patients.

Aged↗