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Effects of age and long term ovariectomy on prolactin secretion, as assessed by the reverse hemolytic plaque assay
1Department of Physiology, University of Maryland, School of Medicine, Baltimore 21201.
Insights
Middle-aged rats show more pituitary cells secreting prolactin (PRL), but not more PRL per cell. Long-term ovariectomy prevents this age-related increase and alters hormone responses.
Area of Science:
- Endocrinology
- Reproductive Biology
- Aging Research
Background:
- Prolactin (PRL) secretion by pituitary lactotrophs is crucial for various physiological processes.
- Aging can influence hormone secretion patterns and cellular responsiveness.
- Estrogen plays a significant role in regulating PRL secretion.
Purpose of the Study:
- To investigate age-related changes in PRL secretion from pituitary lactotrophs in rats.
- To determine if aging affects the number of PRL-secreting cells or the amount of PRL per cell.
- To examine the impact of long-term ovariectomy (LT-OVX) and estradiol (E2) on these age-related changes and hormonal responsiveness.
Main Methods:
- Utilized the reverse hemolytic plaque assay to measure PRL secretion in pituitary cells.
- Compared young, middle-aged, and middle-aged LT-OVX rats, with and without estradiol (E2) treatment.
- Assessed responsiveness to thyrotropin-releasing hormone (TRH) and dopamine (DA).
Main Results:
- Middle-aged rats exhibited a higher percentage of PRL-secreting cells compared to young rats; LT-OVX prevented this increase.
- Basal PRL secretion per cell was similar in young and middle-aged rats but lower in LT-OVX rats.
- TRH stimulated PRL secretion in young and middle-aged rats but not in LT-OVX rats; DA inhibited secretion in LT-OVX rats at lower concentrations.
Conclusions:
- Aging increases the percentage of PRL-secreting cells without altering PRL amount per cell or responsiveness to TRH/DA.
- Long-term estrogen deprivation (LT-OVX) prevents age-related increases in PRL-secreting cells and alters hormonal sensitivity.
- These findings highlight the complex interplay between aging, estrogen, and pituitary lactotroph function.
Abstract:
PRL secretion from pituitary lactotrophs was assessed using the reverse hemolytic plaque assay in young (2- to 3-month-old), middle-aged (10- to 12-month-old), and middle-aged long term ovariectomized (LT-OVX) rats to investigate whether 1) a change in the percentage of pituitary cells secreting PRL is detectable in middle-aged animals, 2) the amount of PRL secreted per cell changes with age, 3) aging involves a change in responsiveness to TRH and/or dopamine (DA), and 4) LT-OVX can prevent any of these changes. Young and middle-aged rats were OVX for 1 week. LT-OVX rats were OVX at 2-3 months of age and used when they were 10-12 months old. All animals were implanted with Silastic capsules containing estradiol (E2) in sesame oil and killed 3 or 8 days later. Anterior pituitaries were collected, and cells were dispersed and prepared for the reverse hemolytic plaque assay. Three days after E2 was implanted, the percentage of anterior pituitary cells that secrete PRL was higher in middle-aged compared to young rats. LT-OVX prevented this increase; the percentage of cells secreting PRL was significantly lower in LT-OVX than in both young and middle-aged rats. Basal secretion of PRL per cell was not different in young compared to middle-aged rats and was significantly lower in LT-OVX than in either young or middle-aged rats. TRH induced similar increases in plaque size in young and middle-aged rats, but had no effect in LT-OVX rats. DA (10(-7) M) inhibited plaque size only in LT-OVX rats; however, higher concentrations of DA were equally effective in the three experimental groups. Eight days after E2 was implanted, the percentage of cells that secrete PRL increased in LT-OVX rats, but was still significantly lower than that in middle-aged animals. After 8 days of E2 treatment, PRL release was similar in the three experimental groups under basal conditions. In LT-OVX rats TRH produced a small increase in PRL secretion (30-40%); DA suppressed PRL release in a similar manner in the three groups. These data demonstrate that middle-aged rats exhibit an increase in the percentage of cells secreting PRL without a concomitant detectable change in the amount of PRL released by single cells and/or a change in responsiveness to TRH or DA. Long term estrogen deprivation prevents this age-related change, suppresses responsiveness to TRH, and enhances sensitivity to DA.