Prolactin secretion in healthy adults is determined by gender, age and body mass index

Abstract

Background: Prolactin (PRL) secretion is quantifiable as mean, peak and nadir PRL concentrations, degree of irregularity (ApEn, approximate entropy) and spikiness (brief staccato-like fluctuations).

Hypothesis: Distinct PRL dynamics reflect relatively distinct (combinations of) subject variables, such as gender, age, and BMI.

Location: Clinical Research Unit.

Subjects: Seventy-four healthy adults aged 22-77 yr (41 women and 33 men), with BMI 18.3-39.4 kg/m(2).

Measures: Immunofluorometric PRL assay of 10-min samples collected for 24 hours.

Results: Mean 24-h PRL concentration correlated jointly with gender (P<0.0001) and BMI (P = 0.01), but not with age (overall R(2) = 0.308, P<0.0001). Nadir PRL concentration correlated with gender only (P = 0.017) and peak PRL with gender (P<0.001) and negatively with age (P<0.003), overall R(2) = 0.325, P<0.0001. Forward-selection multivariate regression of PRL deconvolution results demonstrated that basal (nonpulsatile) PRL secretion tended to be associated with BMI (R(2) = 0.058, P = 0.03), pulsatile secretion with gender (R(2) = 0.152, P = 0.003), and total secretion with gender and BMI (R(2) = 0.204, P<0.0001). Pulse mass was associated with gender (P = 0.001) and with a negative tendency to age (P = 0.038). In male subjects older than 50 yr (but not in women) approximate entropy was increased (0.942±0.301 vs. 1.258±0.267, P = 0.007) compared with younger men, as well as spikiness (0.363±0.122 vs. 0463±2.12, P = 0.031). Cosinor analysis disclosed higher mesor and amplitude in females than in men, but the acrophase was gender-independent. The acrophase was determined by age and BMI (R(2) = 0.186, P = 0.001).

Conclusion: In healthy adults, selective combinations of gender, age, and BMI specify distinct PRL dynamics, thus requiring balanced representation of these variables in comparative PRL studies.

Figure 1. Part of the graphic output of the deconvolution analysis in a male control subject, the upper panel shows the original serum PRL concentrations (µg/L) and the fitted concentration curve (interrupted line).

Asterisks denote pulse onsets, and the rhomboids the time of waveform switch. Time 0 min is 0900 hr. The second panel shows the secretion rate in µg/L.min. The third panel represents the secretion rate within bursts (normalized secretion over time) for the daytime (interrupted line) and nighttime (continuous line), stressing the difference in time at which the maximal secretion rate is reached. The lowest plot shows the statistical distribution of the interpulse delays.

Figure 2. Twenty-four hour serum PRL concentration profiles in 41 healthy women and 33 healthy men.

Blood samples were drawn every 10 min. Data are shown as mean, and the bars represent the SEM. The period with lights off (shown as the black horizontal bar) was between 2300 and 0700 h.

Figure 3. Multiple linear regression between age, gender and mean serum PRL concentration.

Data were obtained in 74 healthy subjects, who underwent 24-h blood sampling at 10-min intervals. Male subjects are shown as triangles, female subjects as circles. Data points above the regression plane are open, below they are closed.

Figure 4. Multiple linear regression between age, gender and maximal PRL concentration in the 24-h serum profile.

Data were obtained in 74 healthy subjects, who underwent 24-h blood sampling at 10-min intervals. Male subjects are shown as triangles, female subjects as circles. Data points above the regression plane are open, below they are closed.

Figure 5. Multiple linear regression between age, gender and total logarithmically transformed PRL secretion, calculated by deconvolution analysis.

Data were obtained in 74 healthy subjects, who underwent 24-h blood sampling at 10-min intervals. Male subjects are shown as triangles, female subjects as circles. Data points above the regression plane are open, below they are closed.

Figure 6. Multiple linear regression between age, gender and mean PRL pulse mass, calculated by deconvolution analysis.

Data were obtained in 74 healthy subjects, who underwent 24-h blood sampling at 10-min intervals. Male subjects are shown as triangles, female subjects as circles. Data points above the regression plane are open, below they are closed.

Figure 7. Box plots of the pulsatile PRL secretion during day time and during the period with lights off (2300 -0700 h).

Differences between men and women were calculated with the Kolmogorov-Smirnov test.

Figure 8. Multiple linear regression between age, BMI and the acrophase of the PRL rhythm.

Data points above the regression plane are open, below the plane they are closed. There were no gender differences in acrophase.