Search PubMed⌕ Search

Biomedical subjects

P Kramer

Publications and source records attributed to P Kramer.

At least 127 records · Page 7Linked to original sources
PubMed1985

Precocious ovulation induced by human chorionic gonadotrophin in the immature female rat: comparison of follicle growth induced by treatment with human chorionic gonadotrophin and by electrical stimulation of the hypothalamus.

Precocious first ovulation, preceded by an endogenous preovulatory LH surge, could be predictably induced in immature female rats by administering repeated injections of human chorionic gonadotrophin (hCG). Administration of a dose of 0.05-0.075 i.u. hCG, four times a day from day 28 to day 31 of age resulted in a highly constant ovulatory response: at 4.0 +/- 0.0 days after the start of treatment 7.7 +/- 0.3 (n = 15) ova were found. Use of a higher dose of hCG (0.1 i.u.) resulted in lower numbers of ova (5.6 +/- 0.4, n = 7; P less than 0.005) whereas use of a lower dose of hCG (0.025-0.038 i.u.) resulted in a less constant timing of the induced ovulation at 5.4 +/- 0.2 days after the start of treatment (n = 7; P less than 0.0005). In animals treated with the dose of 0.05-0.075 i.u. hCG, a positive correlation was found between body weight at the start of treatment and the number of ova released (r = 0.75, n = 25; P less than 0.001). Ovarian follicle dynamics were studied on the various days of hCG treatment (dose 0.05-0.075 i.u.) and compared with the follicle changes that take place after electrical stimulation of the hypothalamus, performed on day 28, a treatment known to result in first ovulation 4-5 days later. In both groups a decrease in the number of the smallest and the middle-sized antral follicles as compared with their respective controls was seen, whereas numbers of follicles in the largest, 'ovulatable' size classes gradually increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Changes in ovarian steroidogenesis in prepuberal rats induced to ovulate by low doses of human chorionic gonadotrophin.

To determine whether the decrease in ovarian 5 alpha-reduced androgen production before first ovulation might be caused by an increase in serum LH, prepuberal female rats were injected at 28-31 days of age with low doses of human chorionic gonadotrophin (hCG) (0.05-0.075 i.u., four times daily). This treatment resulted in ovulation of six to ten ova per rat on day 32 in all animals. Treatment with hCG resulted in a gradual decrease in ovarian content and production (i.e. content in ovary and medium after 4h of incubation) of 5 alpha-dihydrotestosterone (DHT) and 5 alpha-androstane-3 alpha, 17 beta-diol. The ovarian content of DHT and the production of 5 alpha-androstane-3 alpha, 17 beta-diol decreased within 24 h after the first injection of hCG. Oestradiol content and production increased between 24 and 48 h after the start of treatment and was maximal on day 31 (day of pro-oestrus). Activities of 5 alpha-reductase and aromatase were measured in ovarian homogenates obtained on days 29-31. Activity of 5 alpha-reductase in hCG-treated rats was lower than that in control rats on all days studied. Aromatase activity in hCG-treated rats increased between days 29 and 31. It was concluded that multiple injections of low doses of hCG, which may induce ovulation, cause a decrease in 5 alpha-reduced androgen production, which is probably due to a decrease in 5 alpha-reductase activity. The subsequent increase in oestradiol production corresponds with an increase in aromatase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgens↗
PubMed1985

Inhibin-like activity in ovarian homogenates of prepubertal female rats and its physiological significance.

The presence and physiological significance of ovarian inhibin-like activity (ILA) in immature rats was studied by measuring ILA in ovarian homogenates and by studying the short-term changes in serum concentrations of FSH and LH after unilateral or bilateral ovariectomy. Inhibin-like activity in ovarian homogenates was estimated using an in-vitro bioassay system with dispersed rat anterior pituitary cells and subsequent measurement of FSH and LH levels in the spent pituitary cell medium. Inhibin-like activity, expressed in units/ovary, was undetectable in 13-day-old ovaries, was present in 18-day-old ovaries (5.8 units/ovary) and rose significantly to a value of 29.1 units/ovary on day 23. Another significant rise was seen between 28 and 33 days of age, with ILA reaching a value of 66.4 units/ovary, a value still well below that found in adult dioestrous ovaries (155.6 units/ovary). In the bioassay no systematic dose-dependent influence on LH secretion was found. Serum concentrations of FSH after unilateral or bilateral ovariectomy at 18 days of age showed no change at 5h and a significant (P less than 0.05) increase compared with sham-operated controls at 24 h after operation. At 23, 28 and 33 days of age significant increases in FSH concentration were seen at 5 and 8 h after both unilateral and bilateral ovariectomy. At 24 h after unilateral ovariectomy, FSH had returned to the control values in these rats, whereas after bilateral ovariectomy a further increase in FSH was seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Recombinant leucocyte interferon A induces steroid-resistant acute vascular rejection episodes in renal transplant recipients.

In an attempt to determine the safety, tolerance, and prophylactic antiviral activity of high doses of recombinant DNA leucocyte interferon A a double-blind parallel-group study was started in 16 renal transplant recipients. All 16 patients had early rejection episodes. In all 8 interferon-treated patients and 1 placebo-treated patient this rejection, which was of the acute vascular humoral type, was steroid resistant. 3 interferon-treated patients also had transient nephrotic syndrome.

Acute Disease↗
PubMed1984

Detection and identification of spatial frequency: models and data.

Detection and identification of up to four simple sinusoidal gratings were studied. The experimental results were quantitatively compared to predictions from several models. The models all assumed probabilistically independent channels sensitive to different ranges of spatial frequency. The models differed in the shapes of their underlying distributions and, for detection, their decision rule. Detection and identification of far-apart spatial frequencies were consistent with these models. Thus, uncertainty effects for both detection and identification (the decrease in performance with an increase in the number of possible spatial frequencies) can be explained without assuming that attention capacity is limited.

Attention↗
PubMed1984

Effect of influenza vaccine on warfarin anticoagulation.

Recent studies have indicated that viral infections, influenza vaccination, or drugs that increase interferon synthesis all decrease hepatic drug metabolism. We report a case in which influenza vaccination was temporally related to an increased anticoagulant effect of warfarin. A prospective study evaluating the effect of influenza vaccination on the prothrombin time of eight patients anticoagulated over the long term showed that there was prolongation of prothrombin time of 40%. In a second study, the effect of influenza vaccination on warfarin t1/2 was determined in healthy subjects. No significant effect on warfarin metabolism was observed after vaccination. We conclude that influenza vaccination is associated with increased anticoagulant response in some patients receiving anticoagulants over a long term. This effect appears to be related to some step in the coagulation pathway and not to decreased warfarin metabolism and a subsequent rise in serum concentration.

Adult↗
PubMed1984

Compensatory ovulatory mechanisms operative after first ovulation in rats unilaterally ovariectomized prepubertally.

Ovarian steroid contents and serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin were measured during the days after first ovulation in rats unilaterally ovariectomized in late prepuberty. In addition, follicle counts were made at second estrus and second metestrus. During the cycle following first ovulation, ovarian estradiol contents in unilaterally ovariectomized (ULO) rats were significantly increased as compared to intact rats on the day of metestrus, on diestrus 1 and on second estrus. Ovarian progesterone was significantly increased on the days of metestrus, on diestrus 1, second proestrus and second estrus, but no differences were seen in ovarian androgen contents. After ULO there was an indication of an augmented FSH surge at the first and the second ovulation. Follicle counts revealed that the total number of healthy as well as of atretic antral follicles on the day of second estrus was significantly increased after ULO, due to increased numbers of the smallest antral follicles. At second metestrus the number of larger antral follicles (350-500 micron 3) and the total number of healthy antral follicles was higher after ULO. It is concluded that the compensatory process after ULO involved increased recruitment of small antral follicles. Activities in the remaining ovary were not simply doubled but a new hormonal balance was established.

Animals↗
PubMed1984

Ovarian steroid concentrations in rats approaching first ovulation.

Steroid concentrations were studied in ovarian tissue obtained by means of unilateral ovariectomy during a 10-day period preceding first ovulation. Furthermore, the levels of progesterone were measured in this period in the serum of simultaneous intact control rats. Ovarian concentrations of testosterone and oestradiol were at about 70 and 15 fmol/mg ovary respectively from 10 to 4 days before first ovulation; they clearly increased to a maximum of 170 and 120 fmol/mg ovary during the last 1-3 days before first ovulation. Ovarian concentrations of 5 alpha-reduced androgens (i.e. androsterone and 5 alpha-androstane-3 alpha,17 beta-diol) were high (up to 2500 fmol/mg ovary) from 7 to 4 days before first ovulation, whereas low levels (500-750 fmol/mg ovary) were present during the last 3 days before ovulation. Both ovarian and serum concentrations of progesterone were constantly low (at 500-1000 fmol/mg ovary and at 17-32 nmol/l respectively) from 10 days to 1 day before first ovulation. An inverse correlation was observed between the ovarian content of 5 alpha-reduced androgens and that of oestradiol, which is in agreement with the existence of a prepubertal shift in pathways of steroid production; this shift seems to take place between 4 and 3 days before first ovulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Androstane-3,17-diol↗
PubMed1983

Changes in serum concentration of luteinizing hormone in the female rat approaching puberty.

Concentrations of LH in the serum were estimated in rats bled either once or twice during a 15-day period preceding first ovulation. In rats bled once (between 09.00 and 17.00 h) serum concentrations showed little change between 15 and 9 days before first ovulation and averaged 16 micrograms/l (days -15 to -9). A shift in LH level, to a mean of 31 micrograms/l, was seen on day -8, whereafter LH concentrations increased gradually. Basal LH values of less than 10 micrograms/l were only found until day -4. The finding that LH values increased with age was confirmed by data from rats bled twice with an interval of greater than or equal to 3 days between bleedings. Furthermore, both in rats bled twice at 11.00 h and in rats bled twice at 15.00 h LH concentrations were significantly higher in the second sample. Both morning (11.00 h) and afternoon (15.00 h) LH concentrations in rats bled once also indicated a rise in LH concentrations with age but it became apparent that only morning values showed a shift in LH concentration (from approximately 15 to approximately 42 micrograms/l) from day -9 to day -8. In contrast, mean afternoon values showed a gradual increase from day -15 on. From day -8 on the number of rats with LH values greater than or equal to 50 micrograms/l increased, and from day -5 on they were more frequent at 15.00 than at 11.00 h. Thus a clear increase in LH secretion, most likely of a pulsatile nature, was found in the female rat approaching puberty. The correlation in time and possible functional relationship with late-prepubertal follicular growth is discussed.

Animals↗