C. Wallaert et Pj. Babin, AGE-RELATED, SEX-RELATED, AND SEASONAL-CHANGES OF PLASMA-LIPOPROTEIN CONCENTRATIONS IN TROUT, Journal of lipid research, 35(9), 1994, pp. 1619-1633
Seasonal variability in physiological parameters can be attributed to
seasonal variations in environmental factors and/or to the consequence
of the presence of endogenous circannual rhythms. In the current stud
y we have measured plasma levels of lipids and of the different lipopr
otein classes in fasting trout (Oncorhynchus mykiss) between the ages
of 5 and 44 months. Independent of age and sexual maturity, a circannu
al variation in the low density lipoprotein concentration between 250
and 1300 mg/dl was demonstrated in both sexes. These seasonal fluctuat
ions might be controlled by an endogenous biological clock synchronize
d by the photoperiod. The lipoprotein profile of trout is dominated by
high density lipoproteins as early as the first months of life. Their
concentration increases progressively during sexual maturation from a
bout 1200 mg/dl in juveniles to about 2500 mg/dl during spermiation or
at the moment of ovulation. This increase is highly significantly cor
related with the increased concentration of testosterone occurring in
both sexes during sexual maturation. The concentration of very low den
sity lipoproteins increases substantially, from about 150 mg/dl to a m
aximal concentration of 800 mg/dl in females and 1100 mg/dl in males,
during the deposit phase of lipid reserves which precedes the rapid in
crease in the gonadosomatic ratio. In the course of rapid ovarian grow
th, vitellogenin appears in the plasma of females and reaches a concen
tration of 2200 mg/dl 1 month before ovulation. From these results it
is concluded that season and reproductive cycle are the two main facto
rs affecting basal plasma lipid and lipoprotein levels in trout. Envir
onmental factors such as photoperiod or endocrine factors such as the
concentration of steroid hormones can be correlated and/or involved in
the regulation of these quantitative variations. These results also s
uggest the presence of an endogenous biological clock able to exert an
independent effect on plasma lipid and lipoprotein levels.