The demonstration of luteinizing hormone releasing factor in hypophysial portal blood of pro‐oestrous and hypophysectomized rats

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Blood was collected from the cut pituitary stalk of male and female rats before and during the application of an electrical stimulus to the medial preoptic area. The plasma was assayed for immunoreactive LH releasing factor (RF) by a double antibody radioimmunoassay using a specific antiserum raised in rabbits against the free acid derivative of the decapeptide LH-RF conjugated to bovine serum albumin. The decapeptide (used as a standard) and pituitary stalk plasma cross-reacted in a similar manner with the antiserum. Stimulation of the preoptic area increased significantly the amount of LH-RF in pituitary stalk plasma in both male and female rats. The increase in LH-RF was linearly related to the strength of the stimulating current, and the amount of LH-RF liberated diminished on cessation of the stimulus. The concentration of LH-RF in pituitary stalk plasma from female rats was significantly greater than that in jugular venous plasma. The magnitudes of the mean increments of LH-RF in pituitary stalk plasma (stimulation minus pre-stimulation values) at various times of the oestrous cycle in female rats suggest that between 18.00 h of dioestrus and 13.00 h of pro-oestrus there is an increase in sensitivity of the LH-RF secretory mechanism to electrical stimulation. However, the increments decreased in magnitude between 13.00 and 18.00 h of pro-oestrus, indicating that the marked increase in responsiveness of the hypothalamo-hypophysial system to electrical stimulation which occurs during this period is due mainly to a change in sensitivity of the pituitary gonadotrophs to LH-RF. The LH-RF in pituitary stalk plasma collected before application of the stimulus was higher at some of the times examined during pro-oestrus than at other times of the oestrous cycle. A higher level of the secretion of the factor may be important for the full development of the priming effect of LH-RF and, consequently, the marked increase in responsiveness of the pituitary gland which occurs during the afternoon of pro-oestrus.

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Immunoreactive Luteinizing Hormone Releasing Factor in Rat Pituitary Stalk Blood: Effects of Electrical Stimulation of the Medial Preoptic Area

Fink¹,

Jamieson²

1976

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“…A hole was then drilled in the frontal bone and a concentric bipolar stimulating electrode (Type SNEX-100; Rhodes Medical Instruments Ltd, Los Angeles, California, U.S.A.) lowered into the preoptic and/or anterior hypothalamic areas (PO/AH; anterior 6-8, lateral 008, depth 8-25; König & Klippel, 1963). The stereotaxic instrument was then inverted to present the ventral aspect of the rat and permit exposure of the median eminence and pituitary stalk by a transpharyngeal approach (Fink, Nallar & Worthington, 1967;). A small hole was cut in the dura with an iridectomy knife and a non-concentric bipolar stimulating electrode (Type SNEX-200; Rhodes Medical Instruments Ltd) was placed on the median eminence so that one pole rested on the mid-line and the other ipsilateral with the PO/AH electrode.…”

Section: Methodsmentioning

confidence: 99%

Electrical Activity of Antidromically Identified Tuberoinfundibular Neurones During Stimulated Release of Luteinizing Hormone and Prolactin in Pro-Oestrous Rats

Dyer¹,

Saphier²

1981

Extracellular activity was recorded from tuberoinfundibular neurones in 28 urethane-anaesthetized pro-oestrous rats. In each rat the electrical activity of one antidromically identified neurone was analysed before and during electrical stimulation in the preoptic/anterior hypothalamic areas (PO/AH). This stimulation (50 Hz, 30 s on and 30 s off for 15 min) resulted in significant increases in plasma concentrations of prolactin (from 46 +/- 11 (S.E.M.) ng/ml before stimulation to 86 +/- 17 ng/ml 20 min later; P less than 0.02) and LH (27 +/- 6 to 48 +/- 11 ng/ml; P less than 0.01). A substantial proportion (11 out of 28) of the tuberoinfundibular neurones was inhibited by PO/AH stimulation. If such cells are directly involved with the secretion of anterior pituitary hormones it is probable that they synthesize and secrete inhibitory factors. We have suggested that cells inhibited by stimulation of the PO/AH are possibly the neurones which secrete prolactin inhibitory factor. The excited cells (eight out of 28) gave complex and variable responses to hypothalamic stimulation and were unable to follow applied stimuli at a ratio of more than one extra action potential for every ten stimulus pulses. We propose that this may explain why it is necessary to stimulate the PO/AH at ten times the frequency required for ovulation to occur following stimulation in the median eminence in anaesthetized pro-oestrous rats.

“…The technique of Worthington (1966), Fink, Nallar & Worthington (1967) and Porter & Smith (1967) was rigidly followed, except that no heparin was injected and that the animal received no blood infusion. With a dental drill, CaCl2 or MgCl2 and ADH release 85 a hole was made in the bone to expose the dura mater between the posterior margin of the optic chiasma and the pons.…”

Section: Methodsmentioning

confidence: 99%

The Release of Antidiuretic Hormone From the Pituitary Stalk After Intravenous Calcium Chloride or Magnesium Chloride Infusion in Rats

Leśnik¹,

Guzek²,

Traczyk³

1969

Experiments were performed on male albino rats in urethane anaesthesia. The pituitary gland was exposed, the pituitary stalk was cut and the whole gland was removed. Isotonic sodium chloride solution used for washing the cut pituitary stalk was collected and its antidiuretic activity assayed. Antidiuretic substance was liberated from the infundibular axons into the washing fluid during continuous intravenous infusion of a hypotonic saline. The antidiuretic activity of the washing fluid was assayed in ethanol-anaesthetized rats. A 5 % sodium chloride solution, infused intravenously to the limit of 1 % of the body weight, caused a significant release of antidiuretic substance from the cut infundibular axons. A similar effect was observed after the i.v. infusion of 1 ml. of a solution containing 0\m=.\06 mM-CaCl2. The i.v. infusion of 0\m=.\02 mM-MgCl2 decreased the amount of antidiuretic substance liberated from the pituitary stalk significantly.