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Biomedical subjects

J D Hoff

Publications and source records attributed to J D Hoff.

9 recordsLinked to original sources
PubMed1983

Hormonal dynamics at midcycle: a reevaluation.

The dynamics of ovarian and pituitary hormone changes during the midcycle period were evaluated. Changes in hormone levels were determined at 2-h intervals for 5 consecutive days during the periovulatory phase of the cycle in five women. During the 50 h preceding the onset of the surge, the rates of increments for estradiol (E2), progesterone (P4), and LH were similar, with doubling times of 57-61 h. The onset of LH and FSH surges was found to occur abruptly (LH doubled within 2 h). They were temporally associated with the attainment of peak E2 levels and occurred 12 h after the initiation of a rapid rise of P4. The mean duration of the surge was 48 h, with a rapidly ascending limb (doubling time, 5.2 h) lasting 14 h accompanied by a rapid decline of E2 and a continued rise of P4. The surge was followed by a peak plateau of gonadotropin levels lasting for 14 h and a transient leveling of P4. The longer descending limb (half-time, 9.6 h), lasting for 20 h, was associated with a second rapid rise of P4, beginning 36 h after surge onset or 12 h before termination of the surge. By using the onset of the LH surge as a reference point, our data provide a relatively precise picture of the hormonal changes preceding the onset of the gonadotropin surge and the temporal relationship between the multiphasic P4 rise and pituitary-ovarian function.

Androstenedione↗
PubMed1982

Comparison of in-vitro bioactivity and immunoreactivity of serum LH in normal cyclic and hypogonadal women treated with low doses of LH-RH.

The in-vitro test of rat interstitial cell testosterone secretion and a radioimmunoassay (RIA) were used to explore the nature of the LH released in women in response to LH-RH. The ratio of in-vitro bioactivity to immunoreactivity (B:I) calculated for serum samples collected from hypogonadal women using the standard LER-907 for comparison was 13.25 +/- 0.56. This mean ratio was significantly elevated (P less than 0.02) above that found for normal cyclic women, 9.48 +/- 0.49. After one i.v. injection of 10 micrograms LH-RH, 5 hypogonadal and 6 luteal-phase women showed an initial significant drop in the B:I ratio (P less than 0.05 and P less than 0.02 respectively) followed by a steady significant rise (P less than 0.03; P less than 0.01 respectively). This drop in the B:I ratio as immunoreactive LH rose and the rise in the B:I ratio as immunoreactive LH fell may be the result of the release of two or more kinds of LH, one or more with a slower in-vivo clearance rate and an increased B:I ratio.

Female↗
PubMed1981

Circadian rhythm in circulating concentration of dihydroxyphenylacetic acid in normal women.

The 24-h patterns of plasma concentration change in dopamine (DA) and its immediate deaminated metabolite, dihydroxyphenylacetic acid (DOPAC), were determined in 6 normal women (16 studies) by a modified radioenzymatic assay. Changes in DOPAC levels exhibited a marked circadian rhythm, with peak during the day and a nadir at night. At 1200 h, the DOPAC concentration increased significantly (P less than 10(-4)) to a peak value 62.9 +/- 8.4 ng/ml) 117% higher than the 24-h mean. At 2200 h, plasma DOPAC decreased (P less than 10(-4)) to a nadir concentration (10.0 +/- 3.3 ng/ml) 66% lower than the 24-h mean. The circadian rhythm of DOPAC could be reproducibly demonstrated over at least 4 successive days in individual subjects. There were no well defined circadian variations in plasma concentrations of DA. Since the plasma DOPAC concentration appears to reflect central nervous system dopaminergic neuronal activity, the present demonstration of a circadian rhythm of plasma DOPAC suggests that the activity of central nervous system DA-containing cells is higher during the day than at night.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1981

Effects of exogenous beta h-endorphin on pituitary hormone secretion and its disappearance rate in normal human subjects.

The disappearance rate of the immunoreactive beta h-endorphin and the effects of beta h-endorphin on pituitary hormone secretion were investigated in normal volunteers. Synthetic human beta h-endorphin was administered as a 2.5-mg iv bolus to five normal women resulting in a 1000-fold increase in concentration of circulating immunoreactive beta h-endorphin within 2.5 min. This was followed by a triple exponential disappearance curve yielding an initial fast component with a half-time (t 1/2; +/-SD) of 4.1 (+/-0.6) min, a midrange component with a t 1/2 of 13.1 (+/-0.6 min, and a slow component with t 1/2 of 46.2 (+/-7.0) min. In both male and female subjects this dose of beta-endorphin induced a significant increase in the levels of PRL and a significant decline in the concentration of LH, without altering basal levels of GH and TSH.

Endorphins↗
PubMed1979

The functional relationship between priming and releasing actions of luteinizing hormone-releasing hormone.

To examine the relationship between the priming and releasing actions of LRF on LH secretion, 14 normal cycling women received 4 different rates of LRF infusion (0.005, 0.01, 0.05, and 0.1 microgram/m2.min for 4 h). The releasing action of the infusion was measured as the area under the curve and the priming effect was assessed by the acute LH increment in response to a test pulse of LRF (10 microgram) at the end of infusion. At the lower 2 infusion rates, there were only minor changes in releasing function, but it increased exponentially (r = 0.986) with higher rates of infusion. In contrast, the priming effect of the lower 2 doses of infusion increased markedly as a function of infusion rate, but no additional priming was found with the higher rates of infusion. Thus, over the range of infusion rates employed, the releasing and priming functions of LRF appear to be dose dependent. These results indicate that the interdependent releasing and priming actions of LRF on LH secretion are functionally dissociable and that large elevations of LRF tend to favor release, while small LRF increments seem to promote priming preferentially.

Adult↗
PubMed1977

The two pools of pituitary gonadotropin: regulation during the menstrual cycle.

Information on the relative activity and on the functional relationships between the acutely releasable (1st) and reserve (2nd) pools of pituitary LH during the course of the normal menstrual cycle was obtained via a 4 h LRF infusion (0.2 mug/min X 4 h). This was immediately followed by 3 pulses of LRF (10 mug at 2 h intervals) to assess further the size of the acutely releasable pool after activation of the reserve pool by the infusion. Our observations indicate that two functional pools of LH are present in all phases of the menstrual cycle and that comparative pool size or activity is influenced profoundly by ovarian steroid feedback as well as by the pattern of input of hypothalamic LRF. From the early to the late follicular phase, in synchrony with the rising levels of E2, the size of the 2nd pool is preferentially augmented. A small increase in the 1st pool activity is not apparent until the late follicular phase when a 5-fold increase in the size of the 2nd pool is also attained. During the mid-luteal phase and in association with relatively high progesterone (P) and E2, th large 2nd pool is maintained as in the late follicular phase but the 1st pool is strikingly smaller. Activation of the 2nd pool of LH by the LRF infusion (priming) increases the acutely releasable LH (1st pool) in all three phases of the cycle, as evidenced by an enhanced response to the 1st but not subsequent pulses of LRF at the end of the infusion as compared with non-infused controls. This priming effect is likely a reflection of activation or "shifting" of LH from the larger 2nd pool to the smaller 1st pool. It is found that this priming effect is greatest during the mid-luteal phase as compared to other phases of the cycle. During the days of mid-cycle LH surge, a dramatic reversal of the relative activity of the two pools in observed and this is manifested by an enormous increase in the activity of the 1st relative to the 2nd pool. In contrast to other phases of the cycle, the release of LH from the 2nd pool is not sustained and this premature decline in LH release despite continuous LRF infusion appears to be due to pituitary depletion of LH as evidenced by the failure of the pituitary response to pulses of LRF immediately following the infusion...

Estradiol↗