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Biomedical subjects

J de Koning

Publications and source records attributed to J de Koning.

At least 127 records · Page 7Linked to original sources
PubMed1979

Studies on a protein synthesis dependent step in LH release by LH-RH.

The hypothesis that LH-RH induces LH release partly through a protein synthesis dependent step (protein factor) was further investigated using two different experimental designs. First, during incubation of pituitary glands of intact dioestrous female rats with a maximally active concentration of LH-RH, the inhibitor of protein synthesis cycloheximide was added at various times after the beginning of the incubation. The results show that it takes a relatively long time, i.e. more than 1 h of exposure to LH-RH before the amount of the protein factor has increased sufficiently to allow a maximal LH secretion. Secondly, LH-RH was injected iv after which the protein factor was assayed by incubating the pituitary glands with a maximally active concentration of LH-RH in the presence of cycloheximide and measuring LH release in vitro. It was found that 1 h after the injection sufficient protein factor was present to permit an elevated response to LH-RH. This response could be suppressed by injecting cycloheximide prior to LH-RH. When the interval between injection of LH-RH and beginning of the incubation was increased to 2 h, LH release in vitro decreased again. However, ovariectomy immediately before LH-RH injection resulted in maintenance of the elevated response toLH-RH in vitro, indicating a role of the ovaries in this phenomenon.

Animals↗
PubMed1978

Refractoriness of the pituitary gland after continuous exposure to luteinizing hormone releasing hormone.

The refractoriness of LH release by pituitary glands from intact female rats was studied during stimulation by luteinizing hormone releasing hormone (LH-RH), monobutyryl cyclic AMP+theophylline or potassium in vitro. Various concentrations of LH-RH (0.1, 0.3 and 10 ng/ml) all caused refractoriness within 24 h. Subsequent exposure to a supramaximally active concentration of LH-RH for 6 h also resulted in a depressed response; the degree of inhibition depended on the concentration of LH-RH to which the glands had been exposed previously. Glands made refractory to LH-RH also showed a depressed response to monobutyryl cyclic AMP+theophylline, although these agents by themselves were unable to induce refractoriness. Incubation in medium containing a high concentration of potassium also resulted in the release of LH, which in all respects was similar to that caused by LH-RH. Glands made refractory to LH-RH showed a decreased response to potassium and, conversely, the release of LH in response to LH-RH was reduced after exposure of glands to potassium. It is concluded that the LH releasing activity of LH-RH, which is mimicked by potassium, deteriorates during continuous exposure to the secretagogue.

Animals↗
PubMed1977

A female patient with "Aase syndrome".

A girl with congenital hypoplastic anemia and triphalangeal thumbs (Aase syndrome) is described. This is the second report of these features is a female patient, making autosomal recessive inheritance a probable explanation.

Anemia, Aplastic↗
PubMed1976

Absence of an inhibitory effect of oestradiol on LH-RH induced release of LH in vitro caused by inhibition of protein synthesis.

Pituitary glands of ovariectomized rats were incubated for four hours and the LH released into the medium was measured by radioimmunoassay at one-hour intervals. The effect of a maximally active dose of LH-RH (1000 mg/ml) on pituitary LH release was inhibited by oestradiol (15 ng/ml) added to the media. Although cycloheximide (25 mug/ml) and puromycin (54 mug/ml) in the medium did not affect LH-RH-induced LH release consistently, the inhibitory effect of oestradiol was prevented. It is concluded that this effect of oestradiol is dependent on de novo synthesis of protein.

Animals↗
PubMed1976

On differences between the preovulatory luteinizing hormone surges of 4- and 5-day cyclic rats.

Preovulatory LH surges were studied in rats with ovarian cycles of 4 days (4d-rats) and 5 days (5d-rats). In 5d-rats the maximal peak height was about twice that observed in 4d-rats, whereas in 4d-rats peaks occurred about 1-5 h later than in 5d-rats and were much less consistently timed. From experiments in which LH releasing hormone (LH-RH) was infused into pentobarbitone-blocked pro-oestrous rats, it was concluded that (a) differences between the two types of preovulatory LH surges originate within the central nervous system, and (b) pro-oestrous LH-RH secretion may not be restricted to the period in which increased LH levels in blood were found, but may exceed this period for a considerable time.

Animals↗