cells decreased to 14 of starting values during the same period. Cells treated with HDL containing high b-carotene on day 1 or days 1 and 3 were then incubated with or without bLH or
dbcAMP for a further 2 days to investigate the effect of bLH and dbcAMP on depletion of b-carotene by luteal cells. b-Carotene depletion in the luteal cells was significantly higher
Ž
. P - 0.05 in LH- and dbcAMP-treated cells than in the control cells in both groups. These results
indicate that the use of solvents such as DMSO or THF may have undesirable effects due to alteration of cell membrane permeability. Supplementation with bLH or dbcAMP may increase the
metabolism of b-carotene in luteal cells. bLH or dbcAMP together with high b-carotene HDL may, when combined with the effect of increased b-carotene metabolism, give less stimulation
than with low b-carotene HDL. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Cattle-feeding and nutrition; b-Carotene; Luteal cells; Lipoprotein; Progesterone
1. Introduction
b-Carotene is present in extremely high concentrations in the bovine corpus luteum Ž
. O’Fallon and Chew, 1984; Holt et al., 1995 , giving the CL its characteristic bright
yellow colour. As well as acting as a precursor for vitamin A, there is increasing evidence that b-carotene may be necessary for optimal steroid production, possibly
Ž .
acting as an anti-oxidant Young et al., 1995 . It has been reported previously that Ž
b-carotene may affect luteal cell steroid production in vitro Pethes et al., 1985; .
Ž .
O’Shaughnessy and Wathes, 1988 and in vivo Dembinski and Bronicki, 1994 . On the Ž
. other hand, Graves-Hoagland et al. 1988 found that a positive relationship existed
between in vitro bovine luteal cell progesterone production and plasma b-carotene during the winter when plasma b-carotene concentrations are low in dairy herds. They
showed that during the summer when plasma b-carotene is increased, this relationship is lost. In addition, some studies in dairy cattle have failed to observe an effect of
Ž b-carotene supplementation on plasma steroid hormone levels Folman et al., 1979;
. Wang et al., 1982 .
Ž .
b-Carotene may also be required for normal ovarian function. Inaba et al. 1986 showed that the levels of plasma b-carotene are significantly lower in cows with ovarian
cysts than those in normal cows, when they are raised on a feed with low b-carotene content. It has also been reported that b-carotene supplemented cows have a much lower
Ž incidence of ovarian cysts than unsupplemented cows Lotthammer and Ahlswede,
. 1977 .
There is evidence that b-carotene may have an effect on follicular development in the Ž
. bovine. Mayer et al. 1975 observed that ovulation occurred about 1 day after the onset
of oestrus in the b-carotene supplemented group, but not until 2 days after the onset of Ž
. oestrus in the deficient group. Their result was later confirmed by Schams et al. 1977 ,
who found that the time interval between the occurrence of the LH peak and ovulation was more than doubled in the b-carotene deficient animals They also reported that the
maximum delay in ovulation after the occurrence of the LH peak was 72.5 and 49 h in b-carotene deficient and supplemented groups, respectively.
b-Carotene is normally transported to the ovary incorporated in the lipid component Ž
. of high density lipoprotein HDL in the bovine. Both HDL and low density lipoprotein
Ž .
LDL also supply other fat soluble substances such as cholesterol, vitamin A and Ž
. vitamin E to the corpus luteum Ribaya-Mercado et al., 1993; Aten et al., 1994 .
However, several previous studies have used water miscible solvents such as THF Ž
. Ž
. Bertram et al., 1991 and DMSO Young et al., 1995 to supply b-carotene to cultured
luteal cells. The aim of the present study was to compare the use of THF and DMSO with that of HDL as a mean of supplying b-carotene to luteal cells, and to examine the
interaction between b-carotene and LH and dbcAMP on progesterone production.
2. Materials and methods
