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Biomedical subjects

A M van den Boogaard

Publications and source records attributed to A M van den Boogaard.

4 recordsLinked to original sources
PubMed1989

Is oxytocin present in platelets?

For arginine-vasopressin (AVP) it has been suggested that about 90% of the total amount present in peripheral blood is platelet-membrane bound. Oxytocin (OT) and AVP are nonapeptides which are similar in many respects. We investigated the possibility that OT might be found in platelet-rich plasma samples from patients undergoing ovarian super-stimulation for in-vitro fertilization purposes. These plasma samples were treated with acid repeated freezing/thawing and sonification in an attempt to solubilize or expose the possible bound OT. No differences between OT concentrations in platelet-rich or -poor plasma samples were found. We conclude that plasma OT is not bound or confined to platelets.

Blood Platelets↗
PubMed1983

Follicular development during the luteal phase of the human menstrual cycle.

The aims of the present studies were to determine the number, size range, health, and steroidogenic activities of antral follicles in normal human ovaries during the luteal phase of the menstrual cycle. Steroidogenic activity was assessed from the levels of androstenedione, testosterone, and estradiol in follicular fluid and the levels of extant and FSH-stimulable aromatase activity and FSH-stimulable progestin synthesis in the granulosa cells. Data for luteal phase ovaries were compared to those obtained for ovaries from the late follicular phase. On average, 94% (range, 70-100%) of the luteal phase follicles (greater than or equal to 1 mm diameter) were atretic as assessed by oocyte viability and granulosa cell number. The largest healthy follicles during the mid- to late luteal phase were 4-4.5 mm in diameter; these contained high levels of aromatizable androgen (500-2000 ng/ml), low levels of estradiol (less than 10 ng/ml), and granulosa cells with an extant level of aromatase activity 200 times lower than that in a preovulatory follicle. Based on these biochemical criteria, healthy (luteal phase) follicles were not distinguishable from atretic follicles. Granulosa cells from the luteal phase follicles were responsive to FSH with respect to progesterone and estradiol biosynthetic activity; the aromatase system in the cells from the mid- to late luteal phase follicles was significantly more responsive to FSH than that in cells from late follicular or early luteal phase follicles (P less than 0.05). These data suggest that the number of healthy luteal phase follicles (greater than or equal to 1 mm diameter) available for subsequent preovulatory development is limited.

Adult↗
PubMed1980

Alterations in granulosa cell aromatase activity accompanying preovulatory follicular development in the rat ovary with evidence that 5alpha-reduced C19 steroids inhibit the aromatase reaction in vitro.

Locally produced androgens and oestrogens are thought to be important factors in the hormonal regulation of follicular development. In the present study the relationship between follicular maturity and granulosa cell aromatase activity has been examined in vitro. Granulosa cells harvested from the largest antral follicles in adult rat ovaries produced negligible amounts of immunoreactive oestradiol when incubated for 3 h in vitro irrespective of the day of the oestrous cycle upon which they were obtained. However, the addition of aromatizable C19 steroid substrate (testosterone, androstenedione or 19-hydroxyandro-stenedione) to the incubation medium resulted in time- and concentration-dependent increases in oestradiol production which were related to the level of follicular maturity attained in vivo. By measuring oestradiol production using testosterone (10(-7) mol/l) as substrate, the aromatase activity of granulosa cells obtained on the first day of vaginal dioestrus was shown to be only a fraction (less than 5%) of that observed for cells obtained on the morning of pro-oestrus. Cells obtained on the second day of dioestrus displayed an intermediate level of activity which remained approximately five times lower than that of granulosa cells at pro-oestrus. These observations, therefore, establish the induction or activation of granulosa cell aromatase activity as a correlate of normal preovulatory follicular development. However, intrafollicular androgen/oestrogen ratios may also be influenced by quantitative and/or qualitative alterations in the C19 steroidal substrate available for the aromatase reaction. Thus, the naturally occurring non-aromatizable 5alpha-reduced androgen metabolites, 5alpha-dihydrotestosterone and 5alpha-androstanedione, proved to be potent competitive inhibitors of the granulosa cell aromatase reaction in vitro. In this respect each of these biologically active androgens was more effective than 1-enetestololactone, an established C19 steroidal aromatase inhibitor. Since C19 steroid 5alpha-reductase is known to be an ovarian enzyme, it is suggested that by affecting the androgenic/oestrogenic composition of the hormonal milieu, local alterations in the activity of this enzyme may be an additional determinant of preovulatory follicular development and function.

Androgens↗