Biomedical subjects

J C Meijer

Publications and source records attributed to J C Meijer.

9 recordsLinked to original sources

PubMed1992

Pubertal development in the male pig: effects of treatment with a long-acting gonadotropin-releasing hormone agonist on plasma luteinizing hormone, follicle stimulating hormone and testosterone.

The effects of a long-acting gonadotropin-releasing hormone (GnRH) agonist, [D-Trp6]-GnRH (GnRH-A) on developmental profiles of plasma luteinizing hormone (LH), follicle stimulation hormone (FSH) and testosterone (T), and pituitary responsiveness to exogenous GnRH were studied in male Dutch Landrace x Large White crossbred pigs from 1 to 30 wk of age. Group 1 control animals (control; n = 12) were injected subcutaneously in the neck with vehicle at 1 and 16 wk of age. Group 2 animals (early treatment; n = 10) were injected with 600 micrograms [D-Trp6]-GnRH at 1 wk and with vehicle at 16 wk. Group 3 animals (late treatment; n = 8) were injected with vehicle and 3 mg GnRH-A at 1 and 16 wk, respectively. Group 4 animals (early plus late treatment; n = 9) were injected at both 1 and 16 wk with GnRH-A. Blood was collected by brachiocephalic puncture at weekly or biweekly intervals, and through brachiocephalic cannulae, to determine longitudinal profiles of LH, FSH and T, and plasma gonadotropin responses to intravenous injection of GnRH (0.1 microgram/kg), respectively. In control animals, LH and FSH declined over the first 5 wk of postnatal life and peaked again at 10-14 wk. Levels of both hormones were basal from 18 to 30 wk. Plasma T was high in the first week, declined progressively over the next few weeks and remained low until 24 wk when a transient increment was noted. The LH and FSH responses to acute GnRH stimulation were similar at 7 and 14 wk and declined significantly at 23 wk of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Plasma thyrotropin concentration in the male pig: profile from birth to puberty and the effect of season and social environment in the young adult.

Plasma thyrotropin (TSH) secretion was studied in crossbred (Landrace x Large White) immature and young adult Landrace male pigs. Levels of TSH were low over the first 9 wk post-natally and were maximal at 12 wk of age. Thereafter, hormone levels declined and by 16 wk returned to values similar to those at 7 wk. In addition, a transient increase in TSH was noted at 22 wk. A second experiment involved 2 groups of young adult boars housed either in a socially non-restrictive environment (adjacent to estrual females) or a socially restrictive environment (not in direct physical contact with females). TRH stimulated secretion of TSH and the magnitude of this response was affected by month; minimum and maximum responses were found in May and August respectively. There was an effect of social environment on TRH-induced TSH secretion; during February and August, the magnitude of the TSH response to TRH was lower in socially restricted than in socially non-restricted boars.

Aging↗

PubMed1991

Total ligation of the left renal vein in the dog: an inappropriate model for varicocele.

Induction of varicocele was attempted by ligation of the left renal vein (LRV) in male dogs (Group I). Before the operation and in the 4-month post-operative period, sperm count, sperm motility, and sperm morphology of Group I (n = 8) dogs were compared to sham operated animals (Group II, n = 5). Furthermore, haemodynamics as well as testicular and vascular morphology were studied. In Group I, changes in diameter and consistency of the spermatic cord were temporary. Semen quality was reduced significantly during the second month after ligation of the LRV, but improved thereafter. Haemodynamic studies revealed that LRV blood pressure was increased significantly in Group I dogs. An extensive venous collateral network replaced the occluded LRV. Retrograde blood flow in the left testicular vein (LTV) was observed only in the proximal part of the LTV of Group I dogs. In Group II dogs numerous pairs of sufficient valves prevented reflux into the LTV. Histological examination revealed that spermatogenesis was not impaired and that the left pampiniform plexus had not changed. The number of Leydig cells was decreased slightly in Group I dogs. Sufficient valves in the LTV prevented formation of a permanent varicocele.

Angiography↗

PubMed1989

Absence of direct effects of GnRH on testicular steroid secretion in the ram.

Effects of GnRH, administered via the testicular artery, on testicular steroidogenesis were studied in rams during the non-breeding season. Concentrations of testosterone and 17-hydroxyprogesterone in testicular venous blood showed similar profiles which were identical for GnRH-treated (0.5 ng infused over 60 min or 25 ng injected) and control testes. Increases of testicular venous concentration of both hormones were only marginally reflected in peripheral venous concentrations. Peripheral administration of hCG (200 i.u., i.v.) stimulated testosterone secretion to a larger extent than 17-hydroxyprogesterone secretion in 10/11 rams, GnRH-treated and control testes showing identical responses. High testicular venous concentrations of both hormones after administration of GnRH were paralleled by increased concentrations of endogenous LH. These LH peaks were evoked by 25 ng GnRH in 7/8 rams. The observed effects of GnRH treatment on testicular steroid secretion thus cannot be considered to be the result of direct stimulation of steroidogenesis by GnRH.

Animals↗

PubMed1989

[Use of a dental health education center].

In the year 1986 1910 persons made use of the services of a dental health education center in Amsterdam. One day a week a dentist could be consulted. The rest of the week other members of the team were available for answering questions. Almost 30% of the questions concerned dental treatment, diagnosis of treatment plan, 20% dental fees and other financial aspects of treatment and questions for folders, posters et cetera accounted for another 20%. Only 5% of the questions referred to preventive matters. A quarter of the dentist's interventions consisted of giving a second opinion. More women than men, and more privately insured than sick fund insured contacted the center.

Adult↗

PubMed1979

Adrenocortical function tests in dogs with hyperfunctioning adrenocortical tumours.

The response has been studied in nine dogs with hyperadrenocorticism due to adrenocortical tumours to the administration of dexamethasone, insulin, lysine-vasopressin and tetracosactide by measuring the changes in plasma cortisol concentration. Administration of dexamethasone did not produce a decrease in the plasma concentration of cortisol in any of these dogs. Administration of insulin caused slight increases in the plasma concentration of cortisol in four out of eight dogs. Lysine-vasopressin increased the plasma concentration of cortisol in eight out of nine dogs, three responded supranomally. Eight out of the nine dogs responded to tetracosactide administration, three responded supranormally, It is concluded that in the dog, in contrast to man, the lysine-vasopressin test cannot be used to differentiate between pituitary-dependent hyperadrenocorticism and hyperadrenocorticism due to an adenocortical tumour. Apparently pituitary ACTH is not completely depleted in dogs with hyperfunctioning adrenocortical tumours.

Adrenal Cortex Function Tests↗

PubMed1978

Cushing's syndrome due to adrenocortical adenoma in a cat.

An 11-year-old spayed cat was presented with clinical signs suggestive of hyperadrenocorticism. Adrenocortical function was assessed by dexamethasone suppression and by stimulation with ACTH and the results provided a tentative diagnosis of adrenocortical tumour. Via laparotomy (paracostal approach), the enlarged right adrenal gland was removed. Histopathological diagnosis was adrenocortical adenoma.

Adenoma↗

PubMed1978

Biochemical characterization of pituitary-dependent hyperadrenocorticism in the dog.

The biochemical characterization of 22 cases of pituitary-dependent hyperadrenocorticism in the dog, is reported. The principal characteristics of the disease include excessive and non-rhythmic production of cortisol, decreased sensitivity of the hypothalamic-pituitary system to the suppressive effects of dexamethasone, decreased responsiveness of the pituitary-adrenocortical system to the stimulus of insulin-induced hypoglycaemia and increased responsiveness of the system to stimulation with lysine-vasopressin. From these observations it is concluded that pituitary-dependent hyperadrenocorticism in the dog is a valid model for study of the pathogenesis of the disease in man. For the diagnosis of hyperadrenocorticism itself, the measurement of the concentration of corticosteroids in a single sample of plasma obtained 8 h after intravenous injection of 0.01 mg dexamethasone/kg was sufficient. The level of 11-hydroxycorticosteroids was less than 140 nmol/1 plasma in normal dogs, whereas higher values were found in dogs with hyperadrenocorticism. For purposes of differential diagnosis, measurement of the level of corticosteroids in the plasma both before and 4 h after intravenous injection of 0.05 mg dexamethasone/kg is adequage: suppression is obtained only in cases of pituitary-dependent hyperadrenocorticism.

11-Hydroxycorticosteroids↗

PubMed1978

Hypothalamic corticotrophin releasing factor activity in dogs with pituitary-dependent hyperadrenocorticism.

Hypothalamic corticotrophin releasing factor (CRF) activity was determined in five dogs with spontaneous hyperadrenocorticism and in three control animals (one untreated, one treated with high doses of ACTH for 2 months and one treated with high doses of cortisone for 2 months). Hypothalamic CRF activity was low or undetectable in four dogs with Cushing's syndrome due to an adrenocortical tumour. The results are compatible with a pituitary origin for pituitary-dependent hyperadrenocorticism in the dog but are not conclusive; direct information about the rates of hypothalamic CRF secretion is required.

Adrenocortical Hyperfunction↗