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LYSOSOMAL ENZYME RELEASE FROM LUTEINIZEDRAT OVARIES BY PROSTAGLANDIN F2\g=a\

R. WEINER AND G. KALEY

DepartmentofPhysiology,New York MedicalCollege,Valhalla,New York 10595,U.S.A.

(Received24thJanuary1975)

Extensive evidence has been amassed which demonstrates that prostaglandin

(PG)F2\g=a\playsan

importantrole in the

regulationof CL function.

Recently,several experimentalfindingshave buttressed the hypothesisthat PGF2\g=a\is theuterine luteolyticfactor. It has been reportedthat PGF2\g=a\induces degenerationof the CL of the pseudopregnantrat (Pharriss& Wyngarden,1969),and othermammals (Duncan& Pharriss,1970;Kirton et al., 1970;McCracken et al.,1970),that it decreases ovarian progesteronesecretion in pregnantand pseudo-pregnantrats (Behrmanet al.,1971b),and that it is identifiable in uterine venousblood of guinea-pigsand sheeptoward the end of the oestrous cycle,a timewhich coincides with luteal regression(Blandet al., 1971; Blatchleyet al.,1972).Althoughthese aforementioned data clearlydemonstrate the luteolyticproper-ties of PGF2\g=a\,the cellular mechanism(s)by which PGF2\g=a\acts

are

poorlyunderstood. In view of the findingsthat PGF2\g=a\labilizes lysosomesof rat liver(Weiner& Kaley,1972),pancreas, spleenand kidneycortex (Ignarroet al.,1973),and that increased lysosomalenzyme activityoccurs in rat lutein cellsundergoinginvolution (Lobelet al., 1961),the present studywas undertaken todetermine the effects of PGF2\g=a\on acid hydrolaserelease from lysosomesofluteinized ovaries.

In order to obtain large amounts of relativelyuniform luteal tissue, thesuperovulationprocedureof Parlow (1958)was utilized. Immature femaleHoltzman rats 25 to 27 daysold were treated with 50 i.u. PMSG followed 60hr later with 25 i.u. HCG. The excessivelyluteinized ovaries were collected 7daysafter ovulation,pooled,minced in vessels kepton cracked ice and homo-genizedin ice-cold 0-25 M-sucrose buffered to pH 7-4 with 0-01 M-tris usingamotor-driven Teflon pestleand glassmortar. All subsequentpreparativeprocedureswere carried out at 0 to 4C. A modification of the method ofDingle(1961)was employedto harvest lysosomesfrom the resultant homogenates.Ovarian homogenateswere centrifugedat 800 g for 10 min to removenuclei and unbroken cells. The supernatant was then centrifugedat 10,000gfor 20 min to sediment the largegranulefraction containinglysosomes.Thiscrude lysosomalpellet,which also contained microsomes,was resuspendedinbuffered sucrose and its proteinconcentration determined by the method ofLowryet al. (1951),employingbovine albumin as a standard. The suspensionwas then resedimented bycentrifugationat 10,000g for 20 min.

571

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572 R. Weinerand G. KaleyA pairof rat ovaries was taken to provideeach 2-0 ml aliquotof lysosome-

enriched suspensioncontaining1 mg granuleprotein/mlbuffered sucrose. Theselysosomalsuspensionswere incubated with PGF2otor a solution (control)inwhich the PG was dissolved (trimethylolaminomethane,THAM, 6-8 /ig/ml).Incubations were carried out for 30, 60, 90 and 120 min at 37C with gentleshaking.After the incubation,suspensionswere cooled on ice, centrifugedat20,000g for 20 min,and the activityof -glucuronidasereleased into the supernatant was determined. Total -glucuronidaseactivitywas measured in the20,000g supernatant of an aliquotof lysosomalsuspensionwhich had beenexposedto mechanical disruptionin a Virtis homogenizerfor 3 min and tothermal shock by five alternate freeze-thaw cycles.

The activityof -glucuronidase(EC3.2.1.31)was determined at pH 4-5 inacetate buffer utilizingphenolphthaleinglucuronideas the substrate accordingto the procedureof Fishman et al. (1948).Released acid hydrolase,an index of

lysosomalfragility,was calculated in units

of/igphenolphthaleinliberated/mggranuleprotein/hrat 37C,and also expressedas the %of total -glucuronidaseactivity.

Table 1. Effect of PGF2(Z(20^ig/ml)on -glucuronidaserelease fromlysosomalsuspensionsof luteinized rat ovaries

No. of Time of % Total Difference /0Changeexperiments incubation -glucuronidase fromcontrol fromcontrol*

at 37C (min) released15 30 20-070-82t +1-17 + 0-23 +6-2 + 1-2

(2i>

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Enzymereleasefromrat ovarianlysosomes byPGF2a 573Increased activityof lysosomalenzymes is an earlyevent associated with

luteal regression,and undoubtedlyplaysa pivotalrole in the involution of theCL of the rat (Lobelet al., 1961)and the ewe (Deaneet al., 1966).It has, moreover, been shown by Dingleet al. (1968)that lysosomesobtained from sheepCL undergoingregressionexhibit a significantlygreater fragility,as measuredby the release in vitroof lysosomalmarker enzymes in response to a standardphysicalstress, than those obtained from animals in earlyoestrus, or pregnancy.In the lightof these experimentsit was suggestedthat the uterine luteolyticfactor affects lysosomesdirectlyand that the resultant increase in enzyme leakage is perhapsthe primarycause of regressivechangesin the CL.

The abilityof PGF2ato initiate luteolysiswhen administered in vivo(Pharriss& Wyngarden,1969)and its inabilityto do so when incubated with ovariantissue in vitro (Sellner& Wickersham,1970)led to the proposalof a possiblevascular mechanism for PGF2aaction which was thoughtto be mediated byvasoconstriction of the uterine and utero-ovarian veins (Pharrisset al., 1970).It would appear, however,that PGF2c(does not producea sufficient reductionin blood flow to the CL to substantiate this mechanism (Bruce& Hillier,1974).Furthermore,it has recentlybeen demonstrated that PGF2amarkedlyinhibitsprogesterone synthesisby rabbit CL in vitro (O'Gradyet al., 1972).Thesereportssuggesta direct effect byPGF2tton luteal tissue. The studies of Behrmanet al. (1971a)implythat PGF2(tmay producea'biochemical'lesion in the luteincell which results in the lack of adequatestorage of cholesterol esters and theconsequent impairedabilityof the cell to synthesizeprogesterone. The resultsof our studies,showingthat PGF2otlabilizes lysosomesof luteinized rat ovaries,

bridgethe

gapbetween the

previouslyobtained biochemical and

morphologicalfindingsand the putativephysiologicalrole of PGF2aas the uterine luteolyticfactor,and may providean insightinto the mechanism by which PGF2aproducesluteolysisin vivo.

This studywas supportedby a grant from the National Heart and LungInstitute,USPHS. Thanks are due to Dr J. Jewelfor HCG, Dr J. Pike forprostaglandinF2a,Dr A. F. Parlow for PMSG and Mr Asefa Gebrewold for histechnical assistance.

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