Endogenous catecholamines suppress thyrotropin secretion during the early follicular phase of the menstrual cycle.

Abstract

The physiological role of hypothalamic catecholamines in the regulation of TSH secretion in humans has not been studied extensively. We administered the catecholamine synthesis inhibitor alpha-methyl-p-tyrosine (AMPT) to five women in the early follicular phase (one of menstrual cycle days 2-5) of the menstrual cycle and compared TSH secretion patterns to those in five women at the same time in the cycle who did not receive AMPT. From 0800-1600 h, volunteers had an i.v. line placed, through which blood was withdrawn every 15 min for TSH and PRL determinations. AMPT (500 mg) was administered to the study group at 0800 h and again at 1000 h. Baseline TSH concentrations at 0800 h were not significantly different between the control and treatment groups. In keeping with its characteristic circadian secretion pattern, TSH in the control group was 1.72 +/- 0.23 mIU/L at 0800 h, declined to 1.02 +/- 0.11 mIU/L by 1600 h, and was significantly less than the 0800 h value at all time points beyond 1115 h. The decline in TSH was observed in all five controls. By contrast, TSH in the AMPT group rose from an 0800 h value of 1.99 +/- 0.09 mIU/L to a peak of 3.30 +/- 0.86 IU/L by 1245 h, and was significantly higher than that at 0800 h in the treated group from 1130-1315 h. The increase in TSH was observed in all five women who received AMPT. There were significant differences between the mean TSH concentrations in the AMPT-treated (2.51 +/- 0.09 mIU/L) vs. the control group (1.28 +/- 0.09 mIU/L; P < 0.0001) for the entire study. The effectiveness of AMPT was demonstrated by an elevation of mean PRL concentrations from a baseline of 16.67 +/- 2.55 micrograms/L to a peak of 138.7 +/- 21.6 micrograms/L. We conclude that endogenous catecholamines tonically inhibit TSH secretion in the early follicular phase. These data suggest modulation of TRH by tuberoinfundibular dopamine at the hypothalamic and/or pituitary level.

AMPT-induced monoamine depletion in humans: evaluation of two alternative [123I]IBZM SPECT procedures

“…In agreement with previous studies applying the AMPT paradigm in healthy volunteers [ 17 , 29 , 34 , 35 ], AMPT administration increased serum PRL levels significantly shortly after its first administration, and PRL levels fell thereafter, even though more AMPT was administered. AMPT-induced DA depletion consistently produced a two- to ninefold increase in PRL levels [ 17 , 29 , 34 , 35 ]. Previously, PRL has been used as a marker of the effectiveness of AMPT as an inhibitor of endogenous DA synthesis [ 35 ] because hypothalamic DA is known to inhibit PRL release at the level of the pituitary gland [ 36 ].…”

“…AMPT-induced DA depletion consistently produced a two- to ninefold increase in PRL levels [ 17 , 29 , 34 , 35 ]. Previously, PRL has been used as a marker of the effectiveness of AMPT as an inhibitor of endogenous DA synthesis [ 35 ] because hypothalamic DA is known to inhibit PRL release at the level of the pituitary gland [ 36 ]. However, DA is not the only factor controlling PRL levels, and there is no direct relation between hypophysial stalk DA levels and serum PRL levels [ 36 ].…”

Prolonged inhibition of presynaptic catecholamine synthesis does not alter leptin secretion in normal-weight men and women

“…The feasibility of the use of AMPT as a pharmacological clamp of catecholamine activity was confirmed by others (Plosker et al, 1995). Based on these observations it can be concluded that AMPT can induce consistently a biologically significant decrease in catecholamine production and release.…”

Prolonged Inhibition of Presynaptic Catecholamine Synthesis With α-Methyl-Para-Tyrosine Attenuates the Circadian Rhythm of Human TSH Secretion

“…Added in physiolog c blind crossover design in which active and control tests were gic concentrations, exogenous 6-MS was recovered at 81-86%. separated by [4][5][6] weeks. Both tests were performed in women Thentra-ass CVgwas3-8.6% depenineo t concen-…”

“…No crystal formation those of the Diagnostic and Statistic Manual of Mental Disorders, was detected in the urine of any of the subjects studied. by[4][5][6] weeks. Both tests were performed in women Thentra-ass CVgwas3-8.6% depenineo t concen-The intra-assay CV weas 3.3-8.6% depending oi1 the concenduring the early follicular phase of the menstrual cycle (cycle tration, and the interassay CV was 4.9%.…”