I guess the common factor here is the Omega-6 linoleic acid.  Taka

Food Chem Toxicol. 2008 Jan;46(1):259-69. Epub 2007 Sep 11.

Effects of dietary fats and proteins on rat testicular steroidogenic
enzymes and serum testosterone levels.

McVey MJ, Cooke GM, Curran IH, Chan HM, Kubow S, Lok E, Mehta R.
Toxicology Research Division, Health Products and Foods Branch, Food
Directorate, Health Canada, Sir Fredrick G. Banting Research Centre,
2202D1 Tunney's Pasture, Ottawa, ON, Canada K1A 0L2.

It is known that certain dietary fats can modulate rat testosterone
metabolism. In the current study we have investigated testicular
steroidogenic enzyme activities and serum testosterone levels in rats
fed diets containing either different protein sources (casein,
fishmeal, whey) or different lipid sources (soybean oil,
docosahexaenoic acid (DHA), seal oil, fish oil, lard). The diets
examined reflect different marine oils and proteins which are
significant components of Northern Canadian diets. Male rats (42-45
days old, 6 per group), were assigned to specific diets for 42 days.
On the 43rd day of the study, rats were sacrificed and blood plasma
and testes frozen (-80 degrees C) until analysis. Microsomal
steroidogenic enzyme activities (3beta-HSD, 17-OHase, C-17,20-lyase,
17beta-HSD) were measured radiometrically. There were no differences
in enzyme activities between the three dietary protein sources. In
contrast, compared with the standard casein diet, all lipid sources
caused reductions in C-17,20-lyase activity (>50%); seal oil and fish
oil reduced 17-OHase activity (approximately 30%) and soybean oil, DHA
fish oil and lard reduced 17beta-HSD activity (approximately 30%). No
effect on 3beta-HSD activity was evident. Serum testosterone levels
were determined using ELISA kits and were not affected by any diet
with the exception of the soybean oil diet which was significantly
elevated compared with the casein protein diet. Body and testis
weights were not affected by diet. In conclusion, these data
demonstrate that some dietary lipid sources caused reductions in
testicular 17-OHase and C-17,20-lyase activities but not to the extent
that serum T levels were affected, while soybean oil caused elevated
serum testosterone in the absence of elevated steroidogenic enzyme
activities.
PMID: 17936465

Reprod Biol. 2002 Nov;2(3):277-93.

Influence of dietary fatty acids composition, level of dietary fat and
feeding period on some parameters of androgen metabolism in male rats.

Gromadzka-Ostrowska J, Przepiórka M, Romanowicz K.
Department of Dietetics and Functional Foods, Faculty of Human
Nutrition and Consumer Sciences, Warsaw Agricultural University,
Warsaw, Poland.

The aim of the present study was to determine the effect of the
composition of dietary fatty acids, the duration of feeding period and
dietary fat level on androgen metabolism in male rats. One hundred and
twelve Wistar rats were divided into 18 groups which were fed three
diets containing different types of fat (rapeseed [R], palm [P] and
fish [F] oil) at either normal fat level (w/w; 5%) or high fat level
(20%) during one, three or six weeks. Blood plasma level of androgen
(testosterone+dihydrotestosterone) and testicular activity of 17beta-
hydroxysteroid dehydrogenase (17beta-HSD) were investigated. In
addition, androgen content in cytosol of the heart, the target organ,
was measured. Androgen concentration in both blood plasma and heart
cytosol extracts was measured by radioimmunoassay. The activity of
17Beta-HSD was expressed as a conversion of [3H]androstendione to
[3H]testosterone in soluble fraction of gonadal homogenates. Plasma
androgen concentration was influenced by a type of dietary fat
(p<0.05). The highest plasma level of androgen was observed in animals
fed R diets rich in unsaturated fatty acids. Significantly lower
androgen concentration was demonstrated in rats fed P diets rich in
saturated fatty acids. Only the feeding period factor significantly
influenced androgen content in cytosol fraction of heart muscle cells
(p<0.01). A positive correlation was found between plasma androgen
concentration in plasma and cytosol fraction of the heart muscle cells
(r=0.63, p<0.001). The feeding period (p<0.001) and dietary fat type
(p<0.05) significantly affected the activity of 17beta-HSD. The least
17beta-HSD activity was observed in animals consuming the P-20% diet
for six weeks. In summary, dietary fat type and feeding period, but
not fat level, significantly affected both testosterone production and
testosterone uptake by the target organ in male rats. It was found
that a rapeseed diet rich in unsaturated fatty acids stimulated the
testicular function in rats.
PMID: 14666150