2 research outputs found
Determinants of Plasma Androgen and Estrogen Levels in Men
__Abstract__
The steroid hormone testosterone is responsible for the development of the primary and
secondary male sex characteristics such as male pattern hair growth, deepening of the voice
and increased lean body mass. Testosterone is produced in the testicular Leydig cells in
response to stimulation by pituitary derived luteinizing hormone (LH). In its turn the pituitary
LH secretion is regulated by the hypothalamus. Testosterone will feed back onto the pituitary
and hypothalamus thereby allowing the hypothalamo-pituitary-testicular (HPG) axis to
maintain the plasma testosterone concentration within close limits. The serum testosterone
concentration is considered normal when within the reference range as supplied by the
laboratory. The lower limit of this reference range represents the 2.5 percentile of testosterone
levels of a group of apparently healthy men. However, testosterone levels may vary
considerably between individuals.
Older men may have signs and symptoms reminiscent oftestosterone deficiency such as lack
of libido, erectile dysfunction and lower bone and lean body mass. In older men the mean
testosterone concentration in blood is lower compared to young men. The question is whether
the above-mentioned symptoms truly represent testosterone deficiency. For an adequate
answer to this question a better understanding of the determinants ofthe serum testosterone
level in men is necessary in order to better differentiate between normal and abnormal levels
in a specific individual.
In the body testosterone is converted to estradiol. In the past ten years it has become evident
that estradiol is responsible for a number of the effects formerly attributed to testosterone.
Estradiol has an important role in gaining and maintaining bone mass, closing of the
epiphyses and the feedback on gonadotropin release by the pituitary. Since estradiol may be a
determinant of the circulating testosterone concentrations but may also be involved in the
development ofthe clinical syndrome associated with androgen deficiency, evaluation of
estradiol levels in men seems appropriate. However, the interpretation of estradiol levels in
men is probably even more difficult than the interpretation of testosterone concentrations.
Only little is known about the determinants of the estradiol serum concentration in men, its
interaction with testosterone and the minimal tissue level needed to prevent symptoms of
estrogen deficiency.
Therefore, the aim of the present thesis was to gain more insight into the determinants of the
testosterone and estradiol concentrations in men. This information may be helpful when
interpreting the serum testosterone and estradiol concentrations of men with symptoms
reminiscent of androgen deficiency
Hemodynamic and biochemical effects of the AT1 receptor antagonist irbesartan in hypertension
We studied the hemodynamic, neurohumoral, and biochemical effects of the
novel angiotensin type 1 (AT1) receptor antagonist irbesartan in 86
untreated patients with essential hypertension on a normal sodium diet.
According to a double-blind parallel group trial, patients were randomized
to a once-daily oral dose of the AT1 receptor antagonist (1, 25, or 100
mg) or placebo after a placebo run-in period of 3 weeks. Randomization
medication was given for 1 week. Compared with placebo, 24-hour ambulatory
blood pressure did not change with the 1-mg dose, and it fell (mean and
95% confidence interval) by 7.0 (4.2-9.8)/6.1 (3.9-8.1) mm Hg with the
25-mg dose and by 12.1 (8.1-16.2)/7.2 (4.9-9.4) mm Hg with the 100-mg
dose. Heart rate did not change during either dose. With the 25-mg dose,
the antihypertensive effect was attenuated during the second half of the
recording, and wi