Effects of n-3 and n-6 polyunsaturated fatty acids on the growth of fish cells in culture.

chromatography and liquid scintillation counting as described previously 141. Fig. 1 demonstrates a standard curve relating log,,, human proinsulin concentration t o specific activity of HMG-CoA reductase (pmol minI mgI protein). The human proinsulin concentration range for which this curve was linear was 2.7-2.7 x 1 0 5 PM. Thus, the detection limits of the bioassay presently include the physiological concentration range of human proinsulin in serum 161. Having established that a linear response exists between biological activity and proinsulin concentration. the effects o f serum and insulin on the bioassay were examined. Fig. l (h ) shows that the specific activity o f HMG-CoA reductase was significantly elevated ( I ) < 0.05) when serum was present with proinsulin in the medium 1714 k 3 5 3 2 ) pmol min-l mg-' protein1 compared with when proinsulin alone was present [ 160 k 73 (4) pmol minI mg-l protein, m e a n f ~ . ~ . ~ . ( t i ) ] . N o significant difference was observed when insulin ( 100 pM) was present with proinsulin. I t is apparent that there is not only a higher level of activity, but also a greater variation in activity when serum is present. The components in serum, besides proinsulin, responsible for elevating the biological response may include catecholamines, and thyroid hormones, already known to affect cholesterol biosynthesis in liver. This underlies the importance of setting up parallel bioassays when assaying serum samples for proinsulin concentration. Thus this study has shown that a linear biological response can be cstablished for a range of human proinsulin concentrations. This constitutes the first step in the development o f a proinsulin bioassay.