Prolactin (PRL) is a peptide hormone that is involved in a number of diverse
physiologic roles, particularly with respect to reproduction, including: influencing sexual
and parental behaviors, onset of puberty, regulation of seasonal reproduction, follicular
maturation, ovulation, luteinization and corpus luteum (CL) function, steroidogenesis,
mammary gland development and lactation, testicular and spermatozoal function, and
immunomodulation of ovarian processes. Little is known about PRL's role in elephant
reproduction. The present research was conducted to determine seasonal changes in PRL
secretion in non-pregnant female African elephants. A corollary objective was to examine
the potential functional interrelationships between secretions of PRL, cortisol and
progesterone.
Weekly blood samples for 18 months were taken from four female African
elephants and the sera were analyzed by radioimmunoassay for progesterone, cortisol, and
PRL concentrations. Estrous cycles averaged 14 weeks in length, and estrous cycle
synchronicity was evident between pairs of elephants. The luteal phase was defined by
serum concentrations of progesterone consistently above 200 pg/ml, and averaged 9
weeks in length (range: 5-12 weeks) with a mean (�� SE) concentration of 750.3 �� 171.9
pg/ml. The follicular phase was defined by serum concentrations of progesterone
consistently below 200 pg/ml, and averaged 5 weeks in length (range: 4-8 weeks) with a
mean concentration of 103.1 �� 17.5 pg/ml. Mean (�� SE) serum concentration of cortisol
was 5.7 �� 1.3 ng/ml (range: 1.4-19.3 ng/ml), and concentrations of this adrenal steroid
were negatively correlated with progesterone concentrations (r=-0.15; p<0.01). Serum
concentrations of PRL averaged 3.91 �� 0.69 ng/ml (range: 0.84-15.8 ng/ml), were
significantly lower during the luteal phase (p<0.0001; t-test), and were positively
correlated with serum concentrations of cortisol (r=0.14; p<0.05). There was no
significant effect of season on PRL concentrations. One of the elephants appeared to be
hyperthyroid, but since removing her values from the data set did little to affect overall
means, they were included in all of the calculations.
These data suggest that stress may affect secretion of PRL in elephants, and
cortisol and PRL may affect reproductive potential in elephants by altering luteal function.
While this study did not demonstrate a seasonal effect on PRL secretion, it cannot be
concluded that there is none because the reproductive effects of photoperiod are not
always easy to detect. The higher serum concentrations of PRL detected during the
follicular phase suggest that this hormone may play a role in modulating ovarian function
in elephants during this stage of the estrous cycle. / Graduation date: 1998
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33773 |
| Date | 09 January 1998 |
| Creators | Bechert, Ursula S. |
| Contributors | Stormshak, Fredrick |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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