1. The ovulation response to electrical stimulation of the median eminence, or to the intrapituitary infusion of median eminence extract, was observed in control rabbits and animals pre-treated with chlormadinone acetate.2. Chlormadinone acetate pre-treatment did not significantly reduce the proportion of rabbits ovulating in response to electrical stimulation. However, there was a significant reduction in the average number of ruptured follicles when compared with the animals in the control group.3. Chlormadinone acetate pre-treatment significantly reduced the proportion of animals ovulating in response to the intrapituitary infusion of median eminence extract as compared with the control series. However, there was no significant reduction in the average number of ruptured follicles (in those rabbits that ovulated) when compared with the control groups.4. Chlormadinone acetate pre-treatment produced no significant effect upon either the proportion of animals ovulating, or the average number of ruptured follicles, following I.V. injection of 50 mug LH.5. The conclusion drawn is that chlormadinone acetate blocks copulattion-induced ovulation in the rabbit by action at a site in the central nervous system located above the median eminence. The possible effects of chlormadinone acetate upon the secretion of FSH, the pituitary sensitivity to releasing factors and the ovarian sensitivity to LH are discussed.

Animals↗

PubMed1969

A study of the parameters of electrical stimulation of unmyelinated fibres in the pituitary stalk.

1. The milk-ejection response in lactating rabbits has been used to study the effect of electrical stimuli of different types applied to the supraopticohypophysial tract in the pituitary stalk.2. Sine-wave alternating-current pulses were compared with balanced biphasic square-wave pulses of the same frequency and peak-to-peak current strength. At a pulse duration of 2-4 msec the square-wave stimulation was less effective than the sine wave, but at a pulse duration of 8 msec and over, more effective.3. Above threshold levels of 0.12 mA for the current strength, and of 0.5 msec for the pulse duration, the response increased with increasing current strengths to 2.4 mA and increasing pulse durations to 10 msec.4. With constant and effective strength and duration of the pulse a slight diminution of the response was seen as the frequency was diminished from 100/sec to 50/sec. Further diminution in the frequency revealed that at some point between 50 and 10 c/s a sudden abrupt diminution in the magnitude of the responses occurred over a small range of frequency. This was a reversible phenomenon and it is suggested that it may be related to neurosecretory events occurring in the nerve terminals.5. Stimuli with parameters within the ranges mentioned above are effective in eliciting an oxytocic response on the uterus in the rabbit and ovulation responses (when applied to the hypothalamus) in rats and rabbits. It appears likely that stimuli with such parameters are suitable for experiments concerned with stimulation of the hypothalamus.

Animals↗

PubMed1969

Observations on the blood concentration of thyrotrophic hormone (T.S.H.) in schizophrenia and the affective states.

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Adult↗

PubMed1968

Blood-levels of thyrotrophic hormone, protein-bound iodine, and cortisol in schizophrenia and affective states.

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Adolescent↗

PubMed1968

The purification of luteinizing-hormone-releasing factor with some observations on its properties.

Bullock median-eminence tissue was used as a source of luteinizing-hormone-releasing factor for small-scale experiments to explore methods for its isolation. The presence of luteinizing-hormone-releasing factor was detected by the ovulation response in rabbits after intrapituitary infusion of the extract. Gel filtration was found to be suitable for the purification of these extracts. The releasing factor appeared to be a basic peptide of molecular weight in the range 1200-2500. On a larger scale, an extract of hypothalamic tissue from sheep was used to establish a multi-stage isolation procedure that resulted in a 200000-fold purification of luteinizing-hormone-releasing factor. After the initial extraction the isolation process consisted of: (1) two cycles of gel filtration; (2) anion-exchange chromatography; (3) gel filtration in a partially organic medium; (4) thin-layer chromatography on cellulose. Stage (3) separated two zones of activity each containing peptides. One of these was purified further by stage (4) to give a preparation that was active at a dose of 6mug. of peptide/animal, although activity diminished seriously during storage. This preparation contained only five or six components, but the small amounts of peptides obtained at this stage of purity were insufficient for full characterization.

Animals↗

PubMed1968

The site of action of 'chlormadinone acetate' (6-chloro-delta 6-dehydro-17 alpha-acetoxyprogesterone) in blocking ovulation in the mated rabbit.

1. In a study of the site of action of a steroid in current use for contraceptive purposes (6-chloro-Delta(6)-dehydro-17alpha-acetoxyprogesterone; ;chlormadinone acetate'), the ovarian responses [secretion rate of 20alpha-hydroxypregn-4-en-3-one (20 alpha-OH), and the occurrence of ovulation] were observed in control oestrous rabbits and in rabbits following mating, injection of luteinizing hormone, and after electrical stimulation of the median eminence.2. Chlormadinone acetate pretreatment (0.5 mg I.V.) did not lower significantly the secretion of 20 alpha-OH in otherwise untreated oestrous rabbits.3. Chlormadinone acetate, given 24 hr before mating, prevented the rise in 20alpha-OH that would otherwise have occurred, and also blocked the ovulation response following mating.4. Chlormadinone acetate pretreatment did not prevent the ovarian responses to administration of luteinizing hormone.5. Chlormadinone acetate pretreatment did not prevent the ovarian responses to electrical stimulation of the median eminence of the tuber cinereum of the hypothalamus.6. The conclusion is drawn that the chlormadinone acetate block of the ovarian responses following mating is at a site in the central nervous system located above the median eminence.

Anesthesia↗

PubMed1968